Expected Number

Task goals

• Calculate an expected number using Expected Number = probability x number of trials, from a probability given as a fraction, decimal, or percentage.
• Apply the formula to real-world prediction contexts (weather, faulty items, sports success rates, surveys, games of chance).
• Round an expected number sensibly for context (e.g. to the nearest whole trial, or to a stated number of decimal places when the raw value isn't a whole number).
• Find an expected number for the complementary event (e.g. expected tails from a coin's P(Heads)) by first finding the complementary probability.
• Explain that an expected number is an average or estimate, not a guaranteed outcome, and that the actual result can reasonably differ due to random chance.
• Judge whether an actual observed result is a plausible outcome given an expected number, or reason about a decision that depends on the expected number (e.g. whether a stock of prizes will be enough).