SOLUTION: What is the common number should be added to the ratio 1:2 to get7:5?

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Question 1071961: What is the common number should be added to the ratio 1:2 to get7:5?
Answer by ikleyn(52781) About Me  (Show Source):
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Answer. The number is -4.5.

Solution 

Let "x" be the number.


Then you have this equation %281%2Bx%29%2F%282%2Bx%29 = 7%2F5.


Or, after cross-multiplying, 5(1+x) = 7*(2+x).


Simplify and solve it, and you will get x = -4.5.