26/09/2021
When faced with a statistics question that asks for range or inter-quartile range(IQR), the first thing to do is to order your data in ascending order(smallest to largest).
Now think of it as a long slab of of chocolate that you want you to divide into 4 equal parts.
The 4 equal parts are called quartiles and the places where you cut the chocolate are called Q1, Q2 and Q3.
Q2 is also called the median(the middle).
Sometimes a Q-value may lay between two numbers. Simply add the 2 numbers and divide the answer by 2(calculate the average).
Now identify the Q-values for your set of data.
Remember, for a set of data with an odd number of values: once you identified the Q2 value, it can't be used again. So exclude the Q2 when determining the Q1 and Q3 value.
For a data set with an even number of values: the Q2 will be the average between the middle two numbers. Therefore the 2 middle numbers can be used again to determine the Q1 and Q3 values.
To calculate range we use the formula: Range=max-min.
To calculate IQR we use the formula: IQR=Q3-Q1.
The 5 Number summary includes the minimum, Q1,Q2,Q3 and maximum value.
You will use the 5 Number Summary to draw a box-and-whisker plot.
