The sum of the first and second terms of an A.P us 4 and the 10th term is 19. Find the sum of the 5th and 6th terms.

Answer 1

2 a + d = 4

a + 9 d = 19 ... 2 a + 18 d = 38

subtracting equations ... 17 d = 34 ... d = 2 ... a = 1

5th plus 6th ... (a + 4 d) + (a + 5 d) = 2 a + 9 d = ?

Answer 2

2a+9d=2×1+9×2
=2+18=20