Find the sum of all 3 digit whole numbers that are divisible by 13.

3 answers

we have an arithmetic sequence with

a0 = 1st 3-digit number divisible by 13
a0 = 104
d = 13 (why?)
last term is largest divisible by 13 = 988
how many terms? (988-104)/13 + 1 = 69

S = 69/2(104+988) = 37674
MATHS
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