ACT SAT Prep How to determine the the missing value by setting up two proportions

The video tutorial explains how to solve a problem involving soda sizes using ratios. It starts by establishing the ratios between large, medium, and small sodas. The tutorial then demonstrates how to convert large sodas to medium and subsequently medium to small using cross multiplication. The final solution shows that eight large sodas are equivalent to eighteen small sodas.

What mathematical operation is suggested to find the number of small sodas equivalent to a certain number of mediums?

According to the text, how many small beverages are equivalent to eight large sodas?