Question

Petrolyn motor oil is a combination of natural oil and synthetic oil. It contains
3
liters of natural oil for every
4
liters of synthetic oil. If
316
liters of synthetic oil are used, how many liters of Petrolyn oil will be made?

Answer 1

The Petrolyn is 8/13 natural and 5/13 synthetic. If we start with 760 liters of natural oil we can make:

(760 liters Natural) ( 13/8 Petrolyn/Natural ) = 1235 liters Petrolyn

Note how adding the 'units' into the calculation makes it clear what cancels with what in the numerical conversion.