How to calculate Interquartile Range?

Inter quartile range is the variability measure by dividing an ordered dataset into three quartiles. It is used in the calculations of statistics instead of total ranges. Interquartile Range (IQR) is also sometimes called as the middle-fifty or midspread which measures the statistical dispersion of data.

Definition of Interquartile range

When a given set of data is divided into three quartiles based on median of those values, which will be discussed later, IQR can be defined. IQR is defined as the difference of the third or upper quartile (seventy fifth percentile) to the first or lower quartile (twenty fifth percentile) of the data in an ordered range. Half of this range of value is termed as semi-inter quartile range. The Statistics interquartile range is used to summarize the extension of data which is spread. This is considered as more effective than the median or mode values since it shows the range of dispersion rather than a single value.

Steps to Calculate the Interquartile range
Let us consider a dataset having 9 numbers 19, 20, 4, 9,8,11,15,10,12 and calculate the inter quartile range for that.
Step 1: Arrange the given set of data from smallest to largest number. Therefore the order changes to 4,8,9,10,11,12,15,19,20.
Step 2: Find the median of the series. Median is the exact middle number of a series, if the total numbers are odd. If the total number in the set is even, then the average of two middle numbers will be the median. In the above case since total numbers 9 is odd, the 5th data will be the median, which is 11.
Step 3:  Now we have to find the Q1 from left side numbers of the median and Q3 from the right side numbers of the median. From the left side 4 numbers we will get the median as (8+9)/2=8.5, which is Q1.  From the right side numbers we will get the median as (15+19)/2=17, which is Q3.
Step 4: Now, the formula for finding interquartile range is, IQR = Q3-Q1. Therefore we get the IQR as 17-8.5=8.5. Thus 8.5 is the Inter quartile range of the given series.

Thus the separation of quartile decides the value of the IQR and one should be keen on calculating the quartile values.
Alternative definition IQR can also be defined as the distance between the smallest and largest values which are present in the middle 50 percent of the dataset.  Consider a dataset having numbers 1, 3, 4,5,5,6,7,11.  After neglecting the upper and lower quartiles of the dataset, we get the remaining middle numbers as 4,5,5,6. Hence from this the IQR can be calculated as 6-4=2.

Converting Fractions to Decimals

How to Convert Fractions to Decimals
The manual method to convert Fraction to Decimal is by dividing the numerator with the denominator using the long division method for instance, 4/5 here 4 is divided by 5 using the long division method, 4 is a number less than 5 and hence we start with a decimal point in the numerator to make 4 -> 40. Now that the number is 40 using the decimal point we can divide 40 with 5 as 5 x 8 = 40, so the quotient would be 0.8 which is the decimal form of 4/5. Another method used in converting Fractions to Decimals manually is to,
• find the number which when multiplied with the denominator gives a multiple of 10.
• Once the number is found both the numerator and the denominator is multiplied with that number
• The numerator is written with an appropriate placement of the decimal point according to the multiple of 10 in the denominator
For example, 4/5 fraction to decimal first we find the number which when multiplied with 5 gives a multiple of 10. 20 times 5 is equal to 100, so the required number is 20. Now the numerator and the denominator both are multiplied with 20 which gives, 4x20/5x20=80/100, the denominator being 100 the decimal point has to be placed two places towards left from the right which gives .80 or 0.8

When we Convert Fraction to Decimal at times we might not be able to make the denominator a multiple of 10 in such cases an approximate decimal is calculated by multiplying the denominator which  gives the nearest value of multiple of 10, for instance 1/3 and 2/3 fractions to Decimals would be multiplied with 333 in the numerator and denominator which gives 333/999 and 666/999 and the decimal point is placed 3 places towards left from the right as 999 is near to 1000 which has three zeroes, so the approximate decimals are 0.333 and 0.666, the accuracy is only till three decimal places.

To convert Fraction to Decimal using a long division can be given as follows, 2/3 would be 2 divided by 3
2 is less than 3 and hence cannot be divided.  In such case a decimal point is used to make 2,  20. 20 when divided by 3 would be a repeated decimal of 6 which is written as 0.66666…. Rounding of the decimal is done if required.

                                   0.666…  (Goes on)

                                3|20

                                  - 18

                                      20

                                    - 18

                                       20

                                     - 18

                                         2  

Simplifying Fractions

Simplifying Fractions Algebra
Fractions are part of a whole number written as numerator/denominator, the numerator and the denominators are numbers that have factors other than 1 and itself, in short composite numbers. The process of simplifying fractions is a simple method of reducing fractions. Let us now learn how to simplifying fractions which leads to a reduced fraction. In simplifying fractions following are the steps to be followed:
• First we need to find the common factor of the numerator and the denominator. For instance, the common factor of 4 and 8 is 4 as 4 divides both 4 and 8 evenly.
• Next step is to divide the numerator and also the denominator with the common factor of the numerator and the denominator
• The process is to be repeated till there are no common factors for the numerator and the denominator
• Once the composite numbers of the numerator and denominator have no common factors left, the fraction is a reduced fraction or a simplified fraction

Consider the following Simplifying Fractions Examples
Simplify the fraction 48/108,
The common factor of 48 and 108 is 2, dividing 48 and 108 with 2, 48/2=24 and 108/2=54,
The common factor of 24 and 54 is 2, dividing 24 and 54 with 2, 24/2=12 and 54/2=27,
The common factor of 12 and 27 is 3, dividing 12 and 27 with 3, 12/3=4 and 27/3=9.
There are no common factors of 4 and 9 other than 1 and hence the simplified fraction is 4/9

There is another method used in Reducing Fractions or simplifying fractions, it is the GCF method. In this method, the greatest common factor of the numerator and the denominator are found. Then the numerator and the denominator are divided by the greatest common factor which gives the reduced fraction. So, in this method first the largest number that goes exactly into the numerator and the denominator is found,  9/27, here the largest number that divided 9 and 27 exactly is 9 and hence the reduced fraction would be 9x1/9x3= 1/3

Examples of Simplifying Fractions
Simplify the fraction 48/108
The greatest common factor of 48 and 108 is,
48= 2 x 2 x 2 x 2 x 3
108= 2 x 2 x 3 x 3 x 3
The greatest common factor is, 2 x 2 x 3= 12
The numerator and the denominator are divided with the greatest common factor
48/12 = 4 and 108/12=9, the simplified fraction is 4/9 which has no other common factor other than 1

Alternate Interior Angles – Properties and Examples

Definition of Alternate Interior Angles
The Alternate Interior Angles Definition states that if two lines are crossed by a transversal line, then the angles formed in the opposite side of the transversal and in the inner part of the lines at the point of intersection of the lines with the transversal line define Alternate Interior Angles.  Most of the time, the two given lines will be parallel to each other. We can also define Alternate Interior Angles as those corresponding angles which are formed in the inner side of the lines at the point of intersection of a transversal line with those lines.

Properties of Alternate Interior Angles
If the two lines crossed by the transversal are not parallel, then the alternate interior angles formed at the point of intersection of the transversal line with the parallel lines do not have any relationship with one another.  They are just alternate interior angles.

If the two lines crossed by the transversal are parallel, then the alternate interior angles formed at the point of intersection of the transversal line with the parallel lines have equal angle measure.  This means all the alternate interior angles are equal in value. Thus there exists a relationship between the alternate interior angles so formed.

Alternate Interior Angles Examples
For better understanding of the alternate interior angles, let us consider an example. Consider two lines AB and CD lying parallel to each other horizontally.  If a transversal line PQ crosses the two parallel lines, it intersects the line AB at the point E and line CD at the point F. At this point of intersection, a pair of alternate interior angles is formed in the inner part of each line and on the alternate i.e. opposite side of the transversal line.  So, totally two pair of alternate interior angles are formed.

 Among the alternate interior angles, one angle will be obtuse and the other angle will be acute.
Suppose if the alternate interior angle AEF formed in the inner side of line AB is 110 degrees, then as the lines AB and CD are parallel, the alternate interior angle EFD formed in the inner side of the line CD is also 110 degrees. This is based on the property that: in case of parallel lines, the alternate interior angles are equal.  As these two angles are obtuse, the other two alternate interior angles formed will be acute angles of measure 70 degrees (i.e. 180 - 110 = 70).  Therefore, the alternate interior angles BEF = EFC = 70 degrees.

Parallel Lines and their Properties

Parallel Lines Definition
The definition for parallel lines states that if the lines lie in the same plane and if they don’t touch or meet the other lines at any point of the line, then these lines are termed to be parallel lines. If there are two parallel-lines PQ and RS, then it is said that the line PQ is parallel to the line RS.

When are two lines said to be parallel?
Two given lines are said to be parallel-lines if it satisfies any one of the following conditions:
• If they have a pair of alternate interior angles which are of equal measure.
• If they have a pair of corresponding angles which are of equal measure.
• If any one pair of interior angles which lie on the same side of the transversal are supplementary angles.

Constructing Parallel Lines
Now let us see how to construct parallel-lines. Draw a line AB and mark a point C at some place above the line AB.  Through C, draw a transverse line which cuts AB at D. The transverse line crosses C as well as AB. The line can cut the straight line at any angle.  With D as centre and with more than half of CD as radius draw an arc which cuts CD at E and AB at F.  With C as centre and with the same radius, draw a similar arc on the transverse line above the point C to cut the transverse line at G.

Now change the radius. The width of the lower arc that crosses the two lines AB and CD is taken as the compass width i.e. the radius.  With G as centre draw an arc on the upper arc to cut at H. Now a straight line is drawn through C and H.  We can see that the straight line CH is parallel to line AB.

Thus two parallel-lines AB and CH are constructed.

Properties of Parallel Lines
Consider there are two parallel-lines A and B which are cut by a transversal line. At the point of intersection of the transversal line with the two parallel-lines, the following properties will be met:
• The pair of acute angles formed in the parallel-lines is equal.
• The pair of obtuse angles formed in the parallel-lines is equal.
• The acute angles formed are supplementary to the obtuse angles formed.
• Equally measuring alternate interior angles are present.
• Equally measuring corresponding angles are present.
• The sum of the two interior angles which are present on the same side of the transversal is equal to 180 degrees.
• The sum of any acute angle with any obtuse angle is equal to 180 degrees.

Basic understanding of reflex angles

To define reflex angle, let us look at the following figures:

What is it that is different about these angles? Or in other words, what do we notice about these angles? Note that the measures of all the angles are greater than 180 degrees. Based on this understanding we now define reflex-angles as follows: An angle whose measure is more than 180 degrees and less than 360 degrees is called a reflex angle. Mathematically that can be written like this: If an angle measure α is such that, 180 < α < 360 degrees, then α would be a reflex-angle measure.

Now that we know what a reflex-angle is, the next most obvious question would be how can a reflex-angle be measured? Considering the fact that normally we use a set square or a protractor to measure angles, we know that the maximum angle that can be measured using a protractor or a set square is 180 degrees. So how can we measure reflex-angles?

How to measure a reflex angle?
Every normal angle, which is not a reflex-angle, has its corresponding reflex-angle.  Whether an angle is acute or obtuse, it would always have its corresponding reflex-angle. This can be seen in the examples below:
Example 1: 

Here the acute angle is 49 degrees and the corresponding reflex-angle is 311 degrees. The sum of these two angles is 49 + 311 = 360 degrees.
Example 2: 

Here we have an obtuse angle measuring 112 degrees and its corresponding reflex-angle measuring 248 degrees. The sum of these two angles is 112 + 248 = 360 degrees.

Therefore based on the definition of reflex angle, we can state that the sum of an angle and its corresponding reflex-angle is always 360 degrees. Thus if we want to measure a reflex-angle, we follow the following steps:
1. First we measure the corresponding acute or obtuse angle (say 112 degrees or 49 degrees in the above figures) = α degrees.
2. Now subtract the angle thus measured from 360 degrees. Thus our reflex-angle
= r = 360 - α degrees.

Where do we find reflex angles?

Reflex-angles are usually found in concave polygons.

A concave polygon would have at least one reflex-angle. Other examples of concave polygons are shown below:

Here we have a concave quadrilateral, a concave pentagon and a concave heptagon.

Geometry: Alternate interior angles

Definition: Alternate interior angles
Consider a pair of parallel lines is intercepted by a transversal. At each of the intersection points of the lines with the transversal, 4 angles are formed, making a total of 8 angles for the two lines. Each of these angles have a name or significance. Let us try to understand the following example of alternate interior angles.

The above figure shows two black lines intercepted by the red transversal. In the interior of the lines, four angles are formed namely, <5 a="a" also="also" alternate="alternate" and="and" angles.="angles." angles="angles" are="are" called="called" congruent.="congruent." green="green" if="if" interior="interior" is="is" of="of" other="other" p="p" pair="pair" similarly="similarly" the="the" these="these">
Theorem related to alternate interior angles:
When a pair of parallel lines is intercepted by a transversal, each pair of alternate interior angles thus formed are congruent. Therefore in the above figure, angle <5 and="and" angle="angle" congruent="congruent" is="is" p="p" to="to">
Examples of alternate interior angles:
The following pictures show examples of alternate interior angles:
Example 1:

In the above figure, the angles 76 and b are alternate interior angles. Therefore we can say that measure of angle b is 76. Similarly measure of angle a would be 104 since these two are also alternate interior angles and we know that alternate interior angles are congruent.

If one pair of alternate interior angles is acute, then the other pair of alternate interior angles has to be obtuse.  (Note an acute angle is an angle whose measure is less than 90 degrees and an obtuse angle is an angle whose measure is more than 90 degrees but less than 180 degrees)
Example 2:

In the above figure, the parallel lines are intercepted by a horizontal transversal. So here the purple dots are a pair of obtuse alternate interior angles and the pink dots are a pair of acute alternate interior angles. As we already know both the purple angles have to be congruent to each other and similarly both the pink angles also have to be congruent to each other.

Introduction to concept of median

What is median?
Median in math has two meanings. One is the geometric meaning and another is the statistical median.

Geometric median definition:
In a closed plane figure such as a triangle, the line segment that connects the midpoint of one side to the opposite vertex is called the median. See picture below:

The above picture shows a triangle ABC. D, E and F present on the sides AB, BC and CA, so that, AD = DB, CE = EB and AF = FC. The line segments AE, CD and BF are from the triangle ABC. The points where all the three geometric mid-segments intersect is called the centroid of the triangle also called the centre of gravity. In the above figure, O is the centroid of the triangle.

Statistical median definition:

In statistics it is a measure of central tendency. In a frequency distribution, the central value around which most of the values of the variable are centered is called the measure of central tendency. Of the various measures of central tendencies, the most popular are mean, middle number and mode. It is defined as middle value of the data set. For finding median we need to follow the following steps:

1. Arrange the data set in ascending or descending order.
2. If the number of entries is odd, then the middle value would be the (n+1/2)th value.
3. If the number of entries is even, then the middle value would be the average of the (n/2) th and the (n/2 + 1)th value.
4. The value found in step 2 or 3 is called the middle number value.

Sample problem:
1. Find the middle number of the following data set of marks obtained by 10 students in a class test of maximum 10 marks: 8, 8, 9, 5, 5, 6, 6, 7, 6, 4
Solution:
Step 1: Arrange the data in ascending order: 4, 5, 5, 6, 6, 6, 7, 8, 8, 9
Step 2: The number of entries is 10 which is an even number, so we move to step 3.
Step 3: The two middle values would be 10/2 = 5th and 10/2 + 1 = 5+1 = 6th value. Both these are 6. Therefore the middle number is 6.