Civil Service Exam Review · Numerical Ability · Topic 2 · 2 of 4
Ratio and proportion
Share amounts in a given ratio and solve direct and inverse proportions.
1. Ratios
A ratio compares quantities. Simplify it like a fraction: 18:24 = 3:4.
2. Sharing in a ratio
- Add the parts of the ratio.
- Divide the total by that sum to get one part.
- Multiply by each share's number of parts.
Divide ₱1,200 in the ratio 3:5. There are 8 parts, and one part is ₱150. The shares are ₱450 and ₱750.
3. Direct proportion
When one quantity doubles and the other doubles too, set up equal ratios. If 4 pens cost ₱54, one pen costs ₱13.50, so 10 pens cost ₱135.
4. Inverse proportion
When more of one means less of the other, the product stays constant. 6 workers × 10 days = 60 worker-days, so 15 workers need 60 ÷ 15 = 4 days.
Exam tip
To combine a:b and b:c, make the b terms equal first. With 2:3 and 4:5, scale to 8:12 and 12:15, which gives a:c = 8:15.