whats 8/20 into a decimal/percentage

In order to find the decimals you simply divide the two numbers:

$${\frac{{\mathtt{8}}}{{\mathtt{20}}}} = {\mathtt{0.4}}$$

The decimal is 0.4

If you want to find the precentage you take the decimal and multiply it by 100:

$${\mathtt{0.4}}{\mathtt{\,\times\,}}{\mathtt{100}} = {\mathtt{40}}$$

The percentage is 40%

40 percent as a percentage, and 0.40 as a decimal