Grade 7 Probability: Unit Review

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   A number cube was rolled 30 times. Results — 1: 7, 2: 5, 3: 4, 4: 5, 5: 6 and 6: 3. What is the experimental probability of rolling a 1 or a 3?

   1. Experimental probability = number of times it happened ÷ total trials (30).
   2. 1 came up 7 times and 3 came up 4 times: 7 + 4 = 11.
   3. So the experimental probability is 11/30.

   Answer: 11/30

2. Example 2

   A spinner was spun 60 times. Results — blue: 23, red: 10 and green: 27. What is the experimental probability of landing on green?

   1. Experimental probability = number of times it happened ÷ total trials (60).
   2. Green came up 27 times.
   3. So the experimental probability is 27/60, which simplifies to 9/20.

   Answer: 9/20

3. Example 3

   A spinner has 7 equal sections: 2 red and 5 yellow. You spin it twice. What is the probability of spinning red first and then yellow?

   1. The first spin does not change the second — the two spins are independent. There are 7 equal sections, so two spins have 7 × 7 = 49 equally likely outcomes.
   2. P(red) = 2/7 and P(yellow) = 5/7.
   3. Multiply for "and then": 2/7 × 5/7 = 10/49.

   Answer: 10/49