Question

Question 7
Find the sum of first 22 terms of an AP in which d = 7 and ${22}^{nd}$ term is 149.

Answer 1

$d=7a_{22}=149S_{22}=?a_n=a+(n-1)d{a}_{22}=a+(22-1)d149=a+21\times 7149=a+147a=2S_n=\frac{n}{2}(a+a_n)=\frac{22}{2}(2+149)=11\times 151=1661$