Question

find the sum of the first 22nd term of an AP in which d=7 and 22nd term is 149

Answer 1

Given d = 7,
22nd term = 149 ,
⇒ a+21d = 149
⇒a+21(7) = 149
⇒a+147 = 149
⇒a=149-147=2
Sn = (n/2)(2a+(n-1)d)
S₂₂ = (22/2)(2×2+(22-1)7)
S₂₂ = 11(4+21(7))
S₂₂ = 11(4+147)
S₂₂ = 11(151)
S₂₂ = 1661.