Question

The 11^th and 13^th term of an AP are 39 and 45, respectively. What is the common difference of the AP?

Options

• 42

• 21

• 6

• 3

Answer 1

3

Explanation:

Using the AP formula a_n = a + (n − 1)d

11^th term = a + 10d = 39

11^th term = a + 12d = 45

Subtracting the two equations

(a + 12d) − (a + 10d) = 45 − 39

2d = 6 ⇒ d = 3

Thus, the common difference d = 3