Question

You use 3 cans of soup to serve 5 people. If you want to serve 20 people, what should you do?

Answer 1

Most of the information’s that are required are already given in the question.
The number of cans used to serve 5 people = 3
Then
The number of cans required to serve 1 people = (3/5) * 1
                                                                             = (3/5) cans
So
The number of cans required to serve 20 people = (3/5) * 20 cans
                                                                               = 3 * 4 cans
                                                                               = 12 cans
So 12 cans will be required to serve 20 people. I hope the procedure is clear enough for you to understand.

Answer 2

If you would like to know how many cans of soup you will need, you can calculate this using the following steps:

3 cans of soup ... 5 people
x cans of soup = ? ... 20 people

3 * 20 = 5 * x    /5
x = 3 * 20 / 5
x = 12 cans of soup

The correct result would be 12 cans of soup.