Question

The sum of two numbers is $30$. Then find one of the number, given that the product of those two numbers are maximum ?

• A. $20$
• B. $12$
• C. $10$
• D. $15$

Answer 1

The correct option is D $15$

Let one number be $x$ then other will be $30-x$
Product of the numbers,
$P=x(30-x)=30x-x^2\Rightarrow \frac{dP}{dx}=30-2x=0\Rightarrow x=15$