Question

1. (a) Find the sum of all natural numbers between 250 and 1000, which are exactly
divisible by 7​

Answer 1

Answer:

Clearly the numbers between 250 and 1000 which are divisible by 3 are 252, 255, 258,________ 999.

∴T

n

=999=a+(n−1)d=252+(n−1)3

333=84+n−1

∴n=333−83=250

∴S=

2

n

[a+l]=(250/2)[252+999]

=125×1251=156375.