1. What is the probability of getting a tail when flipping a fair coin?
- A0
- B0.5
- C1
- D0.25
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Answer: B) 0.5
A fair coin has two sides, so the probability of getting a tail is .
Class 9 Probability — practice questions with answers
Statistics · 5 sample questions from the school syllabus. Try each one, then open the answer and the worked solution.
2. If the probability that it will rain tomorrow is 0.85, what is the probability that it will NOT rain tomorrow?
- A0.3
- B0.15
- C0.65
- D-0.35
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Answer: B) 0.15
P(not rain) = 1 - P(rain) = 1 - 0.85 = 0.15, since the two events together are certain.
3. A box contains 90 discs numbered from 1 to 90. If one disc is drawn at random, what is the probability that it bears a two-digit number?
- A0.9
- B0.4
- C1.4
- D1.8
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Answer: A) 0.9
Two-digit numbers from 1 to 90 are 10 to 90, that is 81 numbers. Probability = .
4. In an experiment an event E happened 96 times and the empirical probability of E was 0.32. How many trials were performed altogether?
- A204
- B300
- C30.72
- D396
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Answer: B) 300
P(E) = , so total trials = . (Multiplying instead of dividing gives 30.72, which is not a possible number of trials.)
5. An experiment with exactly three possible outcomes P, Q and R was repeated 300 times. Record of the trials: P 84, Q 126, R 90. Which of the following is true?
- AP(Q) = 0.42, and the three empirical probabilities add up to 3
- BP(Q) = , since Q did not happen in 174 trials
- CP(Q) = 0.42, and the three empirical probabilities add up to 1
- DP(P) = P(Q) = P(R) = , because there are three possible outcomes
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Answer: C) P(Q) = 0.42, and the three empirical probabilities add up to 1
P(P) = , P(Q) = and P(R) = . Their sum is 0.28 + 0.42 + 0.3 = 1, as it must be for a complete list of outcomes. The denominator is always the total number of trials, 300, and the recorded values are not all equal.
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