The median, which can also be known as the second quartile (Q_2), separates the data into upper and lower halves.
The first quartile (Q_1) is the median of the lower half of the data.
The third quartile (Q_3) is the median of the upper half of the data.
Let's identify quartiles of the given data set. In this case the data set i already arranged from least to greatest.
The first quartile is 20 and the third quartile is 45. Since the number of values is even, the median is the average of the two middle values.
Median: 35+ 452= 40
Finally, we can use the values of the first and third quartiles to find the interquartile range (IQR).
Q_3-Q_1=IQR
⇓
45 - 20 = 25
