Find the side of a square whose area is 1600 $m^2$.

The correct option is A 40 m

If the side of square is a, its area is a².

According to question,

$a^2$ = 1600
$a^2$ = 4*4*10*10
a = $\sqrt{\underset{–}{4\ast 4}\ast \underset{–}{10\ast 10}}$
$\downarrow \downarrow \downarrow$
$\text{4}\ast \text{10}$
a = 40 m.