Grade 7 Probability: Simple Probability

Worked examples

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

1. Example 1

   A bag has 8 yellow and 9 blue marbles. You pick one marble without looking. What is the probability of picking blue?

   1. Total outcomes: count everything that could happen, 8 + 9 = 17.
   2. Favorable outcomes: the 9 blue.
   3. Probability = favorable ÷ total = 9/17.
   4. So the probability is 9/17.

   Answer: 9/17

2. Example 2

   A spinner has 4 equal sections: 1 green and 3 yellow. You spin it once. What is the probability of landing on green?

   1. Total outcomes: count everything that could happen, 1 + 3 = 4.
   2. Favorable outcomes: the 1 green.
   3. Probability = favorable ÷ total = 1/4.
   4. So the probability is 1/4.

   Answer: 1/4

3. Example 3

   A bag has 8 yellow, 9 purple and 3 green marbles. You pick one marble without looking. What is the probability of picking yellow?

   1. Total outcomes: count everything that could happen, 8 + 9 + 3 = 20.
   2. Favorable outcomes: the 8 yellow.
   3. Probability = favorable ÷ total = 8/20, which simplifies to 2/5.
   4. So the probability is 2/5.

   Answer: 2/5