If #y=-2# when #x=4#, what is #x# when #y=5#?

Question

#y# varies directly as #x#.

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Answer 1 · 2017-06-20T18:14:59

#x=-10#

Since #y# varies directly with #x#, that means that:

#y/x=#some number. In other words, they have the same ratio.

To solve for #x#, figure out when the ratios equal each other. We'll use:

#y_1/x_1=y_2/x_2#

Plug into the formula:

#-2/4=5/x#

Cross multiply:

#-2x=20#

Divide #-2# on both sides to solve for #x#:

#(-2x)/-2=20/-2#

This results in:

#x=-10#