A recipe calls for 3 cups of flour to make 2 batches of dinner rolls. One batch makes 15 rolls. Laura is making dinner for 12 people and only needs one roll per person. What proportion will help Laura find how much flour is needed to make 12 dinner rolls?
A. 3/30 = x/12
B. 3/2 = x/12
C. 3/15 = x/12
D. 12/15 = x/3

A

Step-by-step explanation:

3 cups of flour produces 2 batches of dinner rolls. So, if one batch makes 15 rolls, then 2 batches makes 30 rolls. Therefore, 3 cups of flour produces 30 rolls.

Laura wants to find how much flour she needs to make 12 rolls.

Here's the setup:

Let x be the number of cups of flour needed. Then,

(3 cups of flour)/(30 rolls)=(x cups of flour)/(12 rolls)

This is the set up for all equations involving ratios. The units should be consistent. Notice how I have flour/rolls=flour/rolls.

It is not necessary to solve the equation, but you should to make sure your answer makes sense. By cross-multiplying, we get x=(3*12)/30 or 1.2 cups.

This solution makes sense. Because 3 cups of flour produces 30 rolls, one cup produces 10 rolls. We need slightly more than 1 cup to get 12 rolls.