Question : If $m^2-n^2=21$ and $m - n = 3$, find the value of $m + n$.
Option 1: 7
Option 2: 4
Option 3: 24
Option 4: 18
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Correct Answer: 7
Solution :
Given, $m^2-n^2=21$ and $m - n = 3$
We know, $m^2-n^2=(m-n)(m+n)$
⇒ $m+n=\frac{m^2-n^2}{m-n}$
⇒ $m+n = \frac{21}{3}$
⇒ $m+n =7$
Hence, the correct answer is 7.
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