Oral contraceptive pills (OCPs) have a typical‑use failure rate of 9 % per year and a perfect‑use failure rate of 0.3 % per year. If 5,000 couples use OCPs with typical use for one year, calculate (a) the expected number of pregnancies and (b) the number of pregnancies avoided if they all used the pills perfectly.

Step-by-step solution

1. Write down the typical‑use failure rate: 9 % = 0.09.
2. Multiply the failure rate by the total number of couples: 0.09 × 5,000 = 450.
3. Thus, 450 pregnancies are expected with typical use.
4. Write down the perfect‑use failure rate: 0.3 % = 0.003.
5. Calculate expected pregnancies under perfect use: 0.003 × 5,000 = 15.
6. Find the difference between typical and perfect outcomes: 450 – 15 = 435.
7. Hence, 435 pregnancies would be avoided if all couples used OCPs perfectly.

Concept tested: Contraceptive failure rates

Published 29 August 2026 · How this solution was prepared and checked

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