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,
![15.5](https://img.qammunity.org/2020/formulas/mathematics/middle-school/61kufalxm6g56eadjfvnbut85pumh9271m.png)
The first quartile is the median of the lower half of the ascending set.
{10,12,14,15}
![Q_1= (12 + 14)/(2) = 13](https://img.qammunity.org/2020/formulas/mathematics/middle-school/rqz5fj0v5s8xye8fssj19b5smv8oyjsg0k.png)
The third quartile is the median of the upper half of the ascending set.
{15.5,17.5,18,19}
![Q_3= (17.5+ 18)/(2) = 17.75](https://img.qammunity.org/2020/formulas/mathematics/middle-school/vgo3lbcm99wut3zj1jgxgxni0xaxw7453b.png)
The inter- quartile range is
![Q_3 - Q_1= 17.75 - 13 = 4.75](https://img.qammunity.org/2020/formulas/mathematics/middle-school/d4mtycfi34cdhakru7cngjf85wbopvnqno.png)