A group of 200 women uses both combined oral contraceptive pills (failure 8 % per year) and male condoms (failure 17 % per year) simultaneously over one year, assuming independent failures. How many pregnancies are expected?
Answer
47
The correct answer is 47 — Expected pregnancies = (200 \times 0.2364 = 47.28), round to 47.
Step-by-step solution
- Calculate probability of success for each method: - Pill success = (1-0.08 = 0.92). - Condom success = (1-0.17 = 0.83).
- Determine joint success probability: (0.92 \times 0.83 = 0.7636).
- Joint failure probability = (1 - 0.7636 = 0.2364).
- Expected pregnancies = (200 \times 0.2364 = 47.28), round to 47.
Common mistake: Adding failure rates instead of using complement rule for independent events
Concept tested: Dual contraceptive failure calculation
Published · How this solution was prepared and checked
← All Reproductive Health questions