Question

find the sum of all those natural number between 100 and 1000 which are completely divisible by 9

Answer 1

use the formula n/2(l+n)
and u will get the answer

Answer 2

108,117..........999,

n=(999-108)/9 + 1,

n=99+1=100,

then
Sum=100/2[2×108+99×9],

sum=50[216+891],

=50×1107,

then
sum=55350