Problem-Solving and Data AnalysisVery hardExpected number from a probability
Problem-Solving and Data Analysis practice question
A factory finds that the probability a randomly selected part is defective is 0.15. If 400 parts are selected at random, how many of them are expected to be defective?
Answer: 60
The expected number is the probability times the number of trials: 0.15 × 400 = 60 defective parts.
Common wrong answers
- If you answered 6
- 6 is 0.015 × 400 — the probability was written as 0.015 rather than 0.15. Fifteen percent of 400 is 60.
- If you answered 15
- 15 is the probability written as a percent. It tells you the rate per hundred; for 400 parts, multiply: 0.15 × 400 = 60.
- If you answered 340
- 340 is the expected number of parts that are NOT defective, 0.85 × 400. The question asks about defective parts.
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