ANSWER
A: 4.75
EXPLANATION
The given date set is
12, 14, 16, 17.5, 10, 18, 15, 15.5, 19
We arrange the data set in ascending order to get,
{10,12,14,15,15.5,16,17.5,18,19}
The median is,
The first quartile is the median of the lower half of the ascending set.
{10,12,14,15}
The third quartile is the median of the upper half of the ascending set.
{15.5,17.5,18,19}
The inter- quartile range is