SOLUTION: The variable Z is directly proportional to X, and inversely proportional to Y. When X is 12 and Y is 4, Z has the value 57. What is the value of Z when X = 18, and Y = 10

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Question 982018: The variable Z is directly proportional to X, and inversely proportional to Y. When X is 12 and Y is 4, Z has the value 57.
What is the value of Z when X = 18, and Y = 10

Found 2 solutions by stanbon, MathLover1:
Answer by stanbon(75887)   (Show Source): You can put this solution on YOUR website!
The variable Z is directly proportional to X, and inversely proportional to Y.
Z = k*X/Y
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When X is 12 and Y is 4, Z has the value 57.
Solve for "k"
57 = k*12/4
k = 19
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What is the value of Z when X = 18, and Y = 10
Z = 19*X/Y
Z = 19*18/10 = 34.2
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Cheers,
Stan H.
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Answer by MathLover1(20850)   (Show Source): You can put this solution on YOUR website!
if the variable is directly proportional to and inversely proportional to , then
When and ,:
Your first sentence:

solve for :


Your second sentence indicates:




since the formula for is:

then the value of, when and , will be:





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