If 7th and 13th term of A.P. are 34 and 64 respectively. Then its 1

1.	If 7th and 13th term of A.P. are 34 and 64 respectively. Then its 18th term is :(A) 89(B) 88(C) 87(D) 90
Answer» Answer is (A) 89 a₇ = 34 (given) a₁₃ = 64 (given) – 6d = -30 d = 5 put the value of d in a + 6d = 34 a + 6 × 5 = 34 a = 34 – 30 a = 4 ∴ a₁₈ = a + 17d = 4 + 17 × 5 = 4 + 85 = 89

If 7th and 13th term of A.P. are 34 and 64 respectively. Then its 18th term is :(A) 89(B) 88(C) 87(D) 90

Answer»

Answer is (A) 89

a₇ = 34 (given)

a₁₃ = 64 (given)

– 6d = -30

d = 5

put the value of d in a + 6d = 34

a + 6 × 5 = 34

a = 34 – 30

a = 4

∴ a₁₈ = a + 17d

= 4 + 17 × 5 = 4 + 85 = 89