Explanation:
What is on sale for 20% off, you would for example have 100% and subtract that 20% of 100%.
100% - 20% = 80%
After that make it as a decimal. To do that all you have to do is move the 80% two decimals to the left. It will give you 0.80.
Then with that 0.80 times it with the regular price, which is 70$.
0.80 x 70 = 56$
Your answer should be 56$. That is going to be your sale price.