dennis has 50 in his bank acount and the interest is 5% how much does he have in his bank acount?

I assume 5% interest is out of $50... so that is 5% of $50 or 5% x $50.

5% can be turned into .05, because percent are numbers out of 100, and $${\frac{{\mathtt{5}}}{{\mathtt{100}}}} = {\frac{{\mathtt{1}}}{{\mathtt{20}}}} = {\mathtt{0.05}}$$.

Then we multiply 0.05 by 50: $${\mathtt{0.05}}{\mathtt{\,\times\,}}{\mathtt{50}} = {\frac{{\mathtt{5}}}{{\mathtt{2}}}} = {\mathtt{2.5}}$$

Our final step is adding that to our orugunal total: $${\mathtt{50}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2.5}} = {\frac{{\mathtt{105}}}{{\mathtt{2}}}} = {\mathtt{52.5}}$$

$52.50.