Question

Find a 20 given that a 3 = 9 and a 8 = 24

Answer 1

a₂₀ = 60

Explanation:

Given :-

a₃ = 9

a₈ = 24

To find :-

a₂₀

Solving :-

Expand the given values.

a + 2d = 9 -(1)

a + 7d = 24 -(2)

Now subtract (1) from (2).

=> 5d = 15

=> d = 3

a = 9 - 2d

a = 9 - 6

a = 3

Final answer :-

a₂₀

= a + 19d

= 3 + 19(3)

= 3+ 57

= 60

a₂₀ = 60