Question

Y varies directly as x. If y =-5 when X= 15, find x when y =3

Answer 1

y varies directly as x,
then y = kx

when y = -5, x =15
so,
-5 = k*15
k = -5/15 = -1/3

so, y = -x/3

when y = 3,
3 = -x/3
x= -3*3
x= -9.