SOLUTION: can you show the steps of solving this problem by cross multiplying (7-2n)/(7+2n)=1/18

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Question 297349: can you show the steps of solving this problem by cross multiplying (7-2n)/(7+2n)=1/18
Found 2 solutions by jim_thompson5910, richwmiller:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
%287-2n%29%2F%287%2B2n%29=1%2F18 Start with the given equation.


18%287-2n%29=1%287%2B2n%29 Cross multiply


126-36n=7%2B2n Distribute.


-36n=7%2B2n-126 Subtract 126 from both sides.


-36n-2n=7-126 Subtract 2n from both sides.


-38n=7-126 Combine like terms on the left side.


-38n=-119 Combine like terms on the right side.


n=%28-119%29%2F%28-38%29 Divide both sides by -38 to isolate n.


n=119%2F38 Reduce.


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Answer:

So the solution is n=119%2F38 which approximates to n=3.132.

Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
This is one reason that many teachers don't like "cross multiplying"
Cross multiplying is a short cut to this
Multiply both sides by 7+2n
Multiply both sides by 18
In cross multiplying you just remove the denominators and multiply the opposite numerator by the denominator
a/b=c/d
multiply c*b and a*d
Multiply the numerator on one side by the denominator on the other side.
Do it again with the other side.
So in the end you should have
(7-2n)*18 = 1*(7+2n)