Symbiosis National Aptitude Test SNAP 2019 Paper

Integers between 113 and 113113 which are divisible by 7 are 119, 126, 133, ..., 113113
This is an A.P. series with first term a = 119
Common difference d = 7
Last term b = 113113
Let n is the number of terms of this series, then form
b = (n – 1)d + a
113113 = 119 + (n – 1)7
(n - 1) = $\frac{113113-119}{7}$ = 16142
∴ n = 16143
Sum of series of A.P.
= $\frac{\mathit{n}}{2}\left[\mathit{a}+\mathit{b}\right]$
= $\frac{16143}{2}\left[119+113113\right]$
= 913952088