Examples of Math Problems: The first and last term of the arithmetic progression are 3 and 21 respectively and the sum of the series is 240. Find the number of terms.

Sunday, January 5, 2014

The first and last term of the arithmetic progression are 3 and 21 respectively and the sum of the series is 240. Find the number of terms.

S%5Bn%5D=%28n%2F2%29%28a%5B1%5D%2Ba%5Bn%5D%29

240=%28n%2F2%29%283%2B21%29

n=240%2F12=20

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