Question

Petrolyn motor oil is a combination of natural oil and synthetic oil. It contains 5 liters of natural oil for every 7 liters of synthetic oil. In order to make 816 liters of Petrolyn oil, how many liters of synthetic oil are needed?

Answer 1

The ratio is 5:7 natural to synthetic.
ratios will always stay the same but can be scaled up or down by some factor.

If we make that factor x then the amount of each would be:

natural oil = 5x
synthetic oil = 7x

together they make 816 L of the mixture petrolyn.

5x + 7x = 816
12x = 816
x = 816/12
x = 68
this is the scaling factor.
synthetic used is: 7x = 7*(68) = 476 L