Question

Find d sum of integers between 100 and 200 that are divisible by 9 annndddddd.... .not divisible by 9

Answer 1

l1) the numbers divisible by 9 from 100 to 200 forms an AP
the AP IS -
108,117,126,....,198
Of the AP :-
first term = 108
common difference= 9
last term = 198
let the number of terms be n
108 + (n-1)9 = 198
9(n -1)= 90
n= 11
Now
sum
= 11/2( 108 + 198)
=11/2 x 306
=1683