3 , 8 , 13 , 18

There are 4 observations, so the median is the mean of the two middle numbers of the arranged set of data. Splitting the observations either side of the median gives two groups of observations. The median of the lower half of data is the lower or first quartile. The median of the upper half of data is the upper or third quartile.

The median of the lower half of data is the lower or first quartile

The median of the upper half of data is the upper or third quartile

Arrange the terms in ascending order.

3,8,13,18

The median is the middle term in the arranged data set. In the case of an even number of terms, the median is the average of the two middle terms.

8+132

Remove parentheses.

8+132

Add 8 and 13.

212

Convert the median 212 to decimal.

10.5

10.5

The lower half of data is the set below the median.

3,8

The median is the middle term in the arranged data set. In the case of an even number of terms, the median is the average of the two middle terms.

3+82

Remove parentheses.

3+82

Add 3 and 8.

112

Convert the median 112 to decimal.

5.5

5.5

Find the Lower or First Quartile 3 , 8 , 13 , 18