1330.11 – Square Mistake!

Instead of finding twice the square of a number, a student whose fingers were all bandaged up found twice the square root. She got the answer 10. What is the correct answer?

Solution

Let $x$ be the number. Then

$2 \sqrt{x} = 10 \leadsto x = 25,$

$2 x^2 = 2 \cdot 25^2 = 2 \cdot 625 = 1250.$

The answer is 1250.