Question

if an arithmetic sequence has its 4th term equal to 8 and its 10th term equal to 20. find its 40th term?

Answer 1

80

Explanation:

nth term = a + d(n - 1)

20 - 8 = 12

(a + d(10 - 1)) - (a + d(4 - 1)) = 12

a + 9d - a - 3d = 12

6d = 12

d = 2

a + 2(4 - 1) = 8

a + 8 - 2 = 8

a = 2

40th term = 2 + 2(40 - 1) = 2 + 78 = 80