SOLUTION: Please assist with the below problem: Suppose y varies directly as x and that y = 21 when x =3. Find the value of y when x = 5

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Question 192574: Please assist with the below problem:
Suppose y varies directly as x and that y = 21 when x =3. Find the value of y when x = 5
Found 2 solutions by Mathtut, solver91311:
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
y%2Fx=k where k is the constant of variation
:
21%2F3=k... k=7
:
y%2F5=7..y=35

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


If y varies directly as x, then



Where k is the constant of proportionality.

You are given that y = 21 when x = 3

So, just substitute the values:



And solve for the value of k.

Now that you have a value for k, you can substitute that value and the given value for x back into the original equation:



And your answer is a simple multiplication of 5 times the value you determined for k.


John