Probability of Combined Events — Year 9 Practice Questions
Work through these Year 9 practice questions on the probability of combined events. Try each one before revealing the worked solution.
Questions
Two coins are flipped. List all the possible outcomes.
Two coins are flipped. Find the probability of getting two heads.
How many outcomes are there when two ordinary dice are rolled?
Two dice are rolled. Find the probability that both show a 6.
A coin is flipped and a dice is rolled. Find the probability of a head and a 4.
Two dice are rolled. Find the probability that the total is 7.
A bag has a red and a blue counter. A counter is taken, replaced, then another is taken. Find the probability of two reds.
The probability a spinner lands on green is 0.4. It is spun twice. Find the probability it lands on green both times.
Answers & Worked Solutions
Question 1 Solution
Step 1: Each coin can be H or T.
Step 2: The outcomes are HH, HT, TH, TT.
Answer: HH, HT, TH, TT
Question 2 Solution
Step 1: There are 4 equally likely outcomes; only HH is two heads.
Step 2: P(two heads) = 1/4.
Answer: 1/4
Question 3 Solution
Step 1: Each dice has 6 outcomes.
Step 2: 6 × 6 = 36.
Answer: 36
Question 4 Solution
Step 1: P(6) on each dice is 1/6.
Step 2: 1/6 × 1/6 = 1/36.
Answer: 1/36
Question 5 Solution
Step 1: P(head) = 1/2 and P(4) = 1/6.
Step 2: 1/2 × 1/6 = 1/12.
Answer: 1/12
Question 6 Solution
Step 1: The pairs giving 7 are (1,6),(2,5),(3,4),(4,3),(5,2),(6,1) — 6 outcomes.
Step 2: 6 out of 36 = 1/6.
Answer: 1/6
Question 7 Solution
Step 1: P(red) = 1/2 each time, and the events are independent.
Step 2: 1/2 × 1/2 = 1/4.
Answer: 1/4
Question 8 Solution
Step 1: The spins are independent, each P(green) = 0.4.
Step 2: 0.4 × 0.4 = 0.16.
Answer: 0.16
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