Question

Find the sum of all three digit natural numbets which are multiples of 7

Answer 1

Answer:

Sum of all three digit natural number divisible by 7 are = 70336.

Step-by-step explanation:

All three digit natural number which are divisible by 7 are 105, 112, 119,.............994. which are in A.P with a = 105, d = 7, l = 994.

let the number of these term be n.

then,

an = 994

à + (n-1)d = 994

105 +(n-1)7 = 994

n = 128

Now, Sn = n/2 (a + l)

Sn = 128/2 (105 + 994)

= 70336.