Question

1.
The sum of all natural numbers between 200 and 400 which are divisible by 7 is
(a) 7,730
(b) 8,729
(c) 7.729
(d) 8.730
in the discible by​

Answer 1

Answer:

• the series is 203,210,217........399
• now the number of terms

$203 + (n - 1)7 = 399 \\ 7n = 399 - 203 + 7 \\ n = \frac{196}{7} \\ n = 28$

• the sum is

$= \frac{28(203 + 399)}{2} \\ = 14 \times 602 \\ =8428$