Question

If the square of the number $A5$ is $X25$, then $X$ is equal to .

• A. $A(A-1)$
• B. $A(A+1)$
• C. $2A+2$
• D. $2A-2$

Answer 1

The correct option is B $A(A+1)$

The square of any number ending with '5' can be obtained easily as follows.

If the number is $A5$, then the end digits of $(A5{)}^2$ are '25' and the number to the left of '25' is $A\times (A+1)$.

For example, the value of ${125}^2$ is
$(12\times 13)25\Rightarrow 15625$

Hence, the value of '$X$' would be $A(A+1)$.