Answer to Question #212452 in Calculus for Chris

Question #212452

how many terms of the arithmetic series 10 + 8 + 6 +... will make the sum 24?

Expert's answer

This is the arithmetic sequence with $a_1=10, d=-2.$

$S_n=\frac{n}{2}(2a_1+(n-1)d)$

$\frac{n}{2}(20-2(n-1))=24$

$n^2-11n+24=0$

$n=3$

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