Question

Given: y varies directly as x. If y = 5 when x = 4, what is the value of y when x = 12?

Answer 1

 y varies directly as x. 
⇒y = kx where k is a constant.

Find k:
When x = 4, y = 5
5 = k(4) 
5 = 4k
k = 5/4

Plug k into the equation:
y = 5/4 k

Find y when x = 12:
When x = 12:
y= 5/4(12)
y = 5(3)
y = 15

Answer: y = 15

Answer 2

Direct Variation: y = kx. Plugging in 5 as y and 4 as x, we get 5 = 4k, k = 5/4.
Now we can find y: y = (5/4)(12) = 15, so y = 15.
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Hope this helps!
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