Tara G.

asked • 02/11/15

4x=3/5 solve for x

A.) Solve this equation by dividing both sides by 4--I did and I came up with .15(3/20)
B.) Solve this equation by multiplying both sides by 1/4--I did this and came up with the same answer as part a
C.) Are any of the above methods valid methods for solving the given equation? In other words, are these methods mathematically legal? Explain?

Vivian L.

4x=3/5
Cross-multiply while bearing in mind that 4x is 4x/1.
(4x)(5)=3
20x=3
x=3/20
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02/11/15

1 Expert Answer

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Norman M. answered • 02/11/15

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To start with, the answer you got for part A and B are correct.
 
Part C wants you to explain why you could do it either way.  I don't think this is a questions I, as a tutor, should give you, but I would be glad to respond to your thoughts.  Look at what you did in A and B, post your thoughts here, and I, or another tutor, would be glad to give you feedback on it.
 
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Tara G.

I'm just confused because I thought you do the opposite to the equation which is dividing. So I wasn't sure if multiplying was an option even though I got the same answer.
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02/11/15

Norman M.

That is a good point...  But if you consider that dividing 4 is the same as multiplying by 1/4, you can get the same answer.
 
So, the question is, can you do whichever method you choose?  The answer is yes, there are multiple ways to solve this problem.  Which is a great thing about math, but sometimes frustrating for students.
 
Let me know if there is anything else I can help you with.
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02/11/15

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