10 , 12 , 15 , 18 , 11 , 13 , 14 , 16 , 19 , 20

There are 10 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.

10,11,12,13,14,15,16,18,19,20

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.

14+152

Remove parentheses.

14+152

Add 14 and 15.

292

Convert the median 292 to decimal.

14.5

14.5

The upper half of data is the set above the median.

15,16,18,19,20

The median is the middle term in the arranged data set.

18

Find the Upper or Third Quartile 10 , 12 , 15 , 18 , 11 , 13 , 14 , 16 , 19 , 20