If y varies directly with x, and If y = 12 when x = 15, how do you find x when y = 21?

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Answer 1 · 2016-02-19T21:57:21

$x=26 1/4$

Use ratios such that $" " (x_1)/(y_1) = (x_2)/(y_2)$

Also note that the condition of 'TRUE' also holds for

$" "(y_1)/(x_1)=(y_2)/(x_2)$

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Need to find $x_2$ so it works much easier if you use $x$ as the numerator, giving:

$" " 15/12 = x/21$

Multiply both sides by 21 and we have:

$" "21xx15/12= x xx21/21$

But $" " 21/21 = 1$ giving:

$" "x=(21xx15)/12 = 26 1/4 " "$ which in decimal form is 26.25