A bin holds 3 bunnies, 5 dogs and 6 bears. A child picks 5 toys at random. What is the probability of choosing exactly 2 bears and 3 dogs?
AIt is 25/1001
BIt is 75/1001
CIt is 63/1001
DIt is 15/1001
Answer & Solution
Correct answer: B. It is 75/1001
1. There are 3 + 5 + 6 = 14 toys in total, and 5 are chosen with order irrelevant.
2. The number of ways to choose any 5 toys is C(14, 5) = 2,002.
3. The bears can be chosen in C(6, 2) = 15 ways.
4. The dogs can be chosen in C(5, 3) = 10 ways.
5. Both selections happen together, so multiply: 15 times 10 = 150 favourable selections.
6. The probability is 150/2,002.
7. Dividing numerator and denominator by 2 gives 75/1,001.
8. Adding rather than multiplying the two counts would give 25 on top, which is the trap when both groups are chosen at once.
_Source: OpenStax Algebra and Trigonometry (CC BY 4.0), Ch 13 "Sequences, Probability and Counting Theory", section 13.7 Probability_
Keep practising Sequences, Probability and Counting Theory
Browse all Sequences, Probability and Counting Theory questions for B.Sc Mathematics, or explore more Mathematics topics.
Related questions
A store has 8 phones and 3 of them are defective. A couple buys 2 phones at random. What iTwo six-sided number cubes are rolled. What is the probability that the sum is greater thaThe probability that a horse wins a race is 1/9. What is the probability that it loses?One card is drawn from a standard deck. What is the probability of drawing a heart or a spWhat makes two events mutually exclusive?One card is drawn from a standard deck. What is the probability of drawing a heart or a 7?When finding the probability that E or F occurs, why is the probability of E and F subtracA fair six-sided number cube is rolled. What is the probability of rolling an odd number?