# What is the perimeter of a rectangle with one side 3cm if it had a area of 21cm?

Sep 13, 2015

The perimeter is 20 cm.

#### Explanation:

Let the one side of the rectangle is $= a$
Let the other side of the rectangle is $= b$
Then area $= a \times b = a b$
Now -

Let $a = 3 c m$
$3 b = 21$
$b = \frac{21}{3} = 7$

The perimeter of the rectangle $= 2 \left(a + b\right) = 2 \left(3 + 7\right) = 2 \left(10\right) = 20$