Question

An economy package of cups has 420 green cups. if the green cups are 20% of the total package, how many cups are in the package?

Answer 1

c(20/100)=420

c=2100

So there were 2100 cups in all.

Answer 2

20 is 1/5 of 100.
If 420 is 1/5 of the total, multiply 420 by 5.
2100 is the total.