To convert a percent to a decimal, we do the opposite of converting a decimal into a percent; instead of multiplying by 100, divide by 100. We can also simply move the decimal point two places to the left.
Let's bust out a visual aid, shall we? 75% represents 75 parts out of 100. We also know that "75 hundredths" represents the decimal 0.75, so they're one and the same.
All we did was move the decimal point at the end of 75% two spots to the left to get 0.75.
Here's one more example. To turn 90% into a decimal, pull the decimal point two spots to the left. It's currently invisible, hiding to the right of the zero.
Now we can see that 90% is the alter-ego of 0.9.
Need more examples? Here ya go:
21% = 0.21
267% = 2.67
5% = 0.05