Question

find the sum of all three digit numbers which are divisible by 11 or multiples of 11​

Answer 1

All the three digit numbers which are multiple of 11 are 110,121,132,..990

Answer 2

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$\underline{\large\mathcal\red{solution}}$

the small 3 digit number is 100 and the larger is 999

now ....

the series is....110,121,132,......,upto990

let 990 is the nth term

now....

990=110+(n-1)11

(990-110+11)/11=n

n=81

therefore the sum of 81 terms is

s(128)=(81/2)(110+990)=44550

therefore the sum is 44550

$\large\mathcal\red{hope\: this \: helps \:you......}$