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2 years ago

11

At summer camp the ratio of boys to girls was 7:2 If there were 21 boys how many girls were there?

1 answer:

Alenkinab [10]2 years ago

3 0

$Ratio:\\7:2\\\\
7x-number\ of\ boys\\2x-number\ of\ boys\\\\
7x=21\ \ \ |:7\\
x=3\\\\
2x=2*3=6\\
Number\ of\ girls\ is\ equal\ to\ 6.$

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Since $a_1,a_2,a_3,\cdots$ are in arithmetic progression,

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$a_1 + a_2 + \cdots + a_n = \displaystyle \sum_{k=1}^n (a_1 + 2(k-1)) \\\\ ~~~~~~~~ = a_1 \sum_{k=1}^n 1 + 2 \sum_{k=1}^n (k-1) \\\\ ~~~~~~~~ = a_1 n + n(n-1)$

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