Question

If a/(a+b) = 15/21, then find (a+b)/(a-b).

Answer:

(a+b)/(a-b) = 7/3.

Given that:
a/(a+b) = 15/21 = 5/7 ...(1)
⇒ a/(a+b) - 1 = 5/7 - 1
⇒ (a-a-b)/(a+b) = (5-7)/7
⇒ -b/(a+b) = -2/7
Adding (1) to the above equation, we get:
-b/(a+b) + a/(a+b) = -2/7 + 5/7
⇒ (a-b)/(a+b) = 3/7
⇒ (a+b)/(a-b) = 7/3.


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