Question

How many terms of the series 1+4+7........will add up to 425?
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Answer 1

17 terms

Explanation:

Let the number of terms be n which will add up to 425.

So, 425=(n/2)*(2+(n-1)*3). 850=n*(3n-1), n=17 or - 50/3 but n can't be negative, so the answer is n=17