Option 1 : 7

**Given: **

3, 12, 5, 7, 12, 18, 8, 13, 7, 3, 14, 2, 10, 9, 15, 14, 6, 18, 11, 15

**Concept: **

Class interval in exclusive form, In this form value of the class interval lower than upper limit and equal or greater than the lower limit.

**Calculation: **

Here, class interval 10 - 15, then the value should be lower than 15 and equal and greater than 10.

Now, we see 12, 12, 13, 14, 10, 14, and 11.

Frequency = 7

**∴ The frequency of the class interval 10 - 15 is 7. **