What is the percent of 40% of 80

You set 40 over 100 because a percentage is just a number in 100 - > 40/100

then, you want to know how much something is out of 80, so you set a variable (x) over 80 - > x/80. Because you want to know the equal value from out of 100 to out of 80, you set these 2 as equal - > 40/100 = x/80

cross multiply:

3200 = 100x

simplify:

32 = x

20 that's the answer