Grade 7 Probability: Experimental Probability

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: 5, 2: 5, 3: 5, 4: 7, 5: 3 and 6: 5. What is the experimental probability of rolling a 2 or a 4?

   1. Experimental probability = number of times it happened ÷ total trials (30).
   2. 2 came up 5 times and 4 came up 7 times: 5 + 7 = 12.
   3. So the experimental probability is 12/30, which simplifies to 2/5.

   Answer: 2/5

2. Example 2

   A spinner was spun 30 times. Results — yellow: 13, blue: 2, red: 8 and green: 7. What is the experimental probability of NOT landing on blue?

   1. Experimental probability = number of times it happened ÷ total trials (30).
   2. Blue came up 2 times, so it did NOT come up 30 − 2 = 28 times.
   3. So the experimental probability is 28/30, which simplifies to 14/15.

   Answer: 14/15

3. Example 3

   A coin was flipped 60 times and landed on heads 32 times. The theoretical probability of landing on heads is 1/2. How much greater is the experimental probability than the theoretical probability?

   1. Experimental probability: heads came up 32 times out of 60, so 32/60.
   2. Theoretical probability: 1/2 = 30/60 — in 60 trials you would expect heads about 30 times.
   3. Subtract: 32/60 − 30/60 = 2/60, which simplifies to 1/30. The experimental probability is that much greater.

   Answer: 1/30