First, work out the difference(increase) between the two numbers you are comparing. So, the difference would be 100-80, which will equal 20.
Then, divide the increase by the original number and multiply the answer by 100. So, that would be 20÷100, which would be 0.2, then it would be 0.2⋅100, so back to 20.
The percent of increase should be 20.
