SOLUTION: So on my test, I missed one question. How did I get this question wrong? If y varies directly as x, and y=30 when x=4, find y when x=-10. (Algebra III; Variation)

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Question 701687: So on my test, I missed one question. How did I get this question wrong?
If y varies directly as x, and y=30 when x=4, find y when x=-10.
(Algebra III; Variation)
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
"y varies directly as x," means y = kx for some number k

y = kx

30 = k*4 ... plug in x = 4 and y = 30

30/4 = k

15/2 = k

k = 15/2

-------------------------------------------------------

y = kx

y = (15/2)x

y = (15/2)*(-10)

y = -150/2

y = -75

So y = -75 when x = -10