# How do you find the partial sum of Sigma 7n from n=51 to 100?

Nov 5, 2017

$x = 7 \cdot \left(51 + 52 + \ldots + 100\right) = 26425$

#### Explanation:

$x = 7 \cdot \left(51 + 52 + \ldots + 100\right)$

=$7 \cdot \frac{100 \cdot 101}{2}$-$7 \cdot \frac{50 \cdot 51}{2}$

=$7 \cdot \left(5050 - 1275\right)$

=$7 \cdot 3775$

=$26425$