CA Foundation · Quantitative Aptitude · Theoretical Distributions
Five independent customers of a Jaipur store each buy on credit with probability 0.2. What is the probability that at least one buys on credit? (Use 0.8^5 = 0.32768.)
The probability of at least one credit buyer is 1 − (0.8)^5 = 1 − 0.32768 = 0.67232. It is easiest to use the complement, the probability that none of the five buys on credit, and subtract it from one.
- A0.67232Correct
- B0.32768
- C0.40960
- D1.00000
Explanation
P(at least one) = 1 − P(none) = 1 − 0.8^5 = 1 − 0.32768 = 0.67232. The value 0.32768 is P(none), which is the complement. The value 0.4096 is P(exactly one) = 5 × 0.2 × 0.8^4 = 0.4096, not at least one.
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