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Expected Frequency

Expected frequency predicts how many times an event should happen, based on its probability and the number of trials.

Predicting a Count

Example 1 — expected frequency of a die roll

A fair die is rolled 300 times. Find the expected number of 6 s . 1 P(rolling a 6) = \frac{1}{6} 2 Multiply by the number of trials: \frac{1}{6} \times 300 Answer: 50

Example 2 — expected frequency of rain

The probability of rain on a given day is 0.2 . In a 30 -day month, find the expected number of rainy days. 1 Multiply: 0.2 \times 30 Answer: 6 days

Practice

A spinner has P(green) = 0.25 . It is spun 80 times. Find the expected number of greens.

Your answer

Predicting a Count

Example 1 — expected frequency of a die roll

A fair die is rolled 300 times. Find the expected number of 6 s . 1 P(rolling a 6) = \frac{1}{6} 2 Multiply by the number of trials: \frac{1}{6} \times 300 Answer: 50

Example 2 — expected frequency of rain

The probability of rain on a given day is 0.2 . In a 30 -day month, find the expected number of rainy days. 1 Multiply: 0.2 \times 30 Answer: 6 days

Practice

A spinner has P(green) = 0.25 . It is spun 80 times. Find the expected number of greens.

Your answer