# The perimeter of a square is given by P=4sqrtA where A is the area of the square, determine the perimeter of a square with the area 225?

May 23, 2017

$P = 60 \text{ units}$

#### Explanation:

Note that $5 \times 5 = 25$. The last digit of which is 5

So what ever we have to square to get 225 will have 5 as a last digit.

${5}^{2} = 25 \textcolor{red}{\leftarrow \text{ Fail}}$

$10 \textcolor{red}{\rightarrow \text{ cant use as it does not end in 5}}$

${15}^{2} \to 15 \left(10 + 5\right) = 150 + 75 = 225 \textcolor{g r e e n}{\leftarrow \text{ This is the one}}$

Thus we have:

$P = 4 \sqrt{225}$

$P = 4 \times 15 = 60$

but to be mathematically correct we should include the units of measurement. AS these are not given in the question we write:

$P = 60 \text{ units}$