#### Question

If the common differences of an A.P. is 3, then *a*_{20} − *a*_{15} is

**A.**5**B.**3**C.**15**D.**20

#### Solution

Let the first term of the A.P. be *a*.

`a_n=a(n-1)d`

`a_20-a_15=[a+(20-1)d]-[a+(15-1)d]`

`=19d-14b`

`=5d`

`=5xx3`

`=15`

The correct answer is C.

Is there an error in this question or solution?

Solution If the Common Differences of an A.P. is 3, Then A20 − A15 is Concept: Sum of First n Terms of an AP.