Probability Example

Grade 7Key Stage 3Årskurs 7-8

Problem

A bag contains 4 red marbles, 3 blue marbles, and 5 green marbles. What is the probability of randomly picking a blue marble?

📝Step-by-Step Solution

Recall the probability formula

Probability = Number of favorable outcomes / Total number of possible outcomes

P(event) = favorable / total

Find the total number of outcomes

Total marbles = 4 red + 3 blue + 5 green = 12 marbles

Total = 4 + 3 + 5 = 12

Find the favorable outcomes

We want blue marbles. There are 3 blue marbles.

Favorable = 3

Calculate the probability

P(blue) = 3/12 = 1/4

Express as decimal or percentage (optional)

1/4 = 0.25 = 25%

P(blue) = 0.25 = 25%

✅Final Answer

P(blue) = 1/4 or 25%

Probability ranges from 0 (impossible) to 1 (certain). A probability of 1/4 means if you picked a marble many times (replacing it each time), about 25% of picks would be blue. Always simplify fractions in probability answers.

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