Lessons · Quantitative Reasoning
CLT Quantitative Reasoning · Lesson
Ratios and proportions
A ratio compares parts. A ratio of 3 to 5 means 3 parts and 5 parts, 8 parts in all. A proportion sets two ratios equal.
- Add the parts of the ratio to get the total number of parts.
- Divide the real total by the number of parts to get the size of one part.
- Multiply to find each group. For proportions, cross-multiply.
Q. The ratio of boys to girls in a class of 40 is 3 : 5. How many boys?
Answer 15
3 + 5 = 8 parts; 40 ÷ 8 = 5 per part; 3 × 5 = 15 boys.
- Treating 3 : 5 as "3 out of 5." The boys are 3 out of 8.
- Setting up a proportion with the units in different places on each side.
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