Question

Find the 40th term of an AP where 12th term is 45 and 17th term is 80.

Answer 1

40th term = 241.

Explanation:

17th term:

= a1 + 16d = 80

12th term

= a1 + 11d = 45 Subtracting the 2 equations:

5d = 80 - 45 = 35

d = 7

and a1 + 16(7) = 80

a1 = 80 -112 = -32.

Therefore the 40th term = -32 + 39*7

= 241.