Multiples of 11 such that they are of 3 -digit and less than 500. 121,132,...,495 cn=
495−121
11
+1=35 S=
35
2
(121+495)=10780 Again, multiplies of 11 which are 3-digits, less than 500 and having 1 at hundred's place are 121,132,...,198 n1=(
198−121
11
)+1=8 S1=
8
2
(121+198)=1276 The multiply of 11 which are of 3 -digits, less than 500 and having 1 at ten's place are 319,418 ∴S2=319+418=737 The multiple of 11 which are 3-digits, less than 500 and having 1 at unit place are 231,341,451 ∴S3=231+341+451=1023 ∴ Required sum =S−S1−S2−S3 =7744