If y varies directly with x and y = -4.5 when x = 13.5, how do you find x when y = 24?

1 Answer
Alan P.
Oct 1, 2015

#x = 72#

Explanation:

If #color(red)(y)# varies directly with #color(blue)(x)# then
#color(white)("XXX")color(red)(y) =c*color(blue)(x)# for some constant #c#

We are told
#color(white)("XXX")color(red)(-4..5) = c*color(blue)(13.5)#

#rarrcolor(white)("X")c = color(red)(-4.5)/color(blue)(13.5) = -1/3#

When #color(red)(y)=color(red)(24)#
#color(white)("XXX")color(red)(24) = (-1/3)color(blue)(x)#

#rarrcolor(white)("X")color(blue)(x) = color(red)(24)*(-3) = 72#

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