Question

The square of $20\frac{1}{5}$ is equal to ____

• A. $408\frac{1}{25}$
• B. $408\frac{25}{1}$
• C. 408
• D. None of the above

Answer 1

The correct option is A

$408\frac{1}{25}$

${\left(20\frac{1}{5}\right)}^2$ can be written as

${(20+\frac{1}{5})}^2$

$=(20{)}^2+{\left(\frac{1}{5}\right)}^2+2\times 20\times \frac{1}{5}\left[\right(x+y{)}^2=x^2+y^2+2xy]$

$=400+\frac{1}{25}+8$

$=408\frac{1}{25}$