hmmm
we use a sequence
all 3 digit numbers divisible by 6
the first one is 102 (16*6)
the biggest one is 996 (166*6)
so we find how many numbers there are because we know a nice summation formula that goes like this
for a sequence that has a first term of a1 and the term we are summing to is an and there are n terms from a1 to an,
the sum is n(a1+an)/2
so
how many terms are there?
16*6 to 166*6
well, hmm
166-16=150 because these are multipules
151 terms (include the 16)
151(102+996)/2=
151(1098)/2=
165798/2=
82899
the sum is 82899
