Nadia thinks of a number - OCR - GCSE Maths - Question 10 - 2020 - Paper 1

Let the number Nadia is thinking of be denoted as $x$.

According to the problem, she finds the square root of $x$ and divides it by 5 to get 20:

$\frac{\sqrt{x}}{5} = 20$

To isolate $\sqrt{x}$, multiply both sides by 5:

$\sqrt{x} = 20 \times 5$

Calculating the right side gives:

$\sqrt{x} = 100$

Next, to find $x$, square both sides:

$x = 100^2$

Thus,

$x = 10000$

Therefore, the number Nadia is thinking of is 10000.