Find out what $M \times B$ is.

Question

Say you have a number $M$. When you take $B\%$ of $M$ and add it to $M$ and then subtract $B \%$ of the new value from itself, you get back $M$.

Find out what $M \times B$ is.

I said let $M=100$ and $B\%=25 \%$ or $B=.25$

So when you do $.25(100)+100=125$ Now, take $.25(125)=31.25$ and do $125-31.25=93.75$ but i am suppose to get back $M$ which I didn't.

Did anyone see what i did wrong or why i am not understanding this problem?

Answer 1

Using variables, your statement is: \begin{align*} M + \frac{B}{100}M - \frac{B}{100}\left(M + \frac{B}{100}M\right) &= M \\ -\left(\frac{B}{100}\right)^2M &= 0 \\ B^2M &= 0 \end{align*} Hence, $B$ or $M$ must be zero so that $M \times B = 0$.