1 Answer

Brett Pontarelli · Answer 1 · 2020-07-13T12:27:50+0000

Each term in the sum differs by 6, so that the
th term is determined by
4+6(n-1) . The last term is 70, so there are

$4+6(n-1)=70\implies n=12$

terms in the sum. If

$S=4+10+\cdots+64+70$

then it's also true that

$S=70+64+\cdots+10+4$

and joining the sums gives us

$2S=(4+70)+(10+64)+\cdots+(64+10)+(70+4)$

$2S=12\cdot74$

$S=\frac{12\cdot74}2\implies\boxed{S=444}$

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