Question

If the common differences of an A.P. is 3, then a₂₀ − a₁₅ is 

Options

• A. 5

• B. 3

• C. 15

• D. 20

Answer 1

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.