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Alex C.

asked • 05/13/16

Finding variable value in formulas

1. r=2s—2t. Solve for t. When I try to solve, I get (2s—r)/(2) but the book says the answer is s—(r/2) 
 
 
2. (A/P) = B—1. Solve for B. Again, when I try to solve I get (A/P)+1 and the book says its (a+p)/(p) 

Nathan B.

I can help you with your first one, at least.
 
r = 2s - 2t
factor out a 2:
r = 2(s - t)
Divide both sides by 2:
r/2 = s - t
Subtract s from both sides:
r/2 - s = -t
Multiply both sides by -1:
s - r/2 = t


Here's what I think you did:
r = 2s - 2t
r - 2s = -2t
(r - 2s) / -2 = t
(2s - r) / 2 = t


Your answers are essentially the same. Check out what happens when you take your answer and divide by that two in the denominator:
2s/2 - r/2 = t
s - r/2 = t
Now your answer looks exactly like the one in the book--they divided that 2 into the numerator that you have.
 
The second formula eludes me at the moment, though, so I can't advise on that, hence why this is in comment section instead of the answer.
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05/13/16

2 Answers By Expert Tutors

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Michael J. answered • 05/13/16

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Effective High School STEM Tutor & CUNY Math Peer Leader

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