Question

Find the 20th term of the A.P. whose 7th term is 24 less than the 11th term, first term being 12.

Answer 1

T₁₁ – T₇ = 24
a= 12
Let a be the first term and d be the common difference, then
(a + 10d) – (a + 6d) = 24
a + 10d – a – 6d = 24
⇒ 4d = 24
⇒ d = `(24)/(4)` = 6
a = 12
∴ T₂₀ = a + 19d
= 12 + 19 x 6
= 12 + 114
= 126.