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2 years ago

Find the sum of all 3 digit whole numbers that arw divisible by 13 ?

1 answer:

7 0

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

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