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Grade 9 Probability Quiz

Chance, Predictions and Evidence
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What this quiz covers

Grade 9 Probability Quiz 1 draws its questions at random from a bank of 10 questions, with full worked solutions for every one.

Worked examples

A few of the question types, with full solutions, so you know what to expect.

What is the probability of an event that is \(\text{impossible}\)?

  1. \(0\)
  2. \(0.5\)
  3. \(1\)
  4. \(-1\)

Answer: \(0\)

\(\text{The probability scale runs from } 0 \text{ to } 1.\)

\(\text{An impossible event has probability } 0.\)

A fair die is rolled once. Find \(P(\text{even})\).

  1. \(\frac{1}{2}\)
  2. \(\frac{1}{3}\)
  3. \(\frac{2}{3}\)
  4. \(\frac{1}{6}\)

Answer: \(\frac{1}{2}\)

\(\text{Even outcomes: } 2, 4, 6 \rightarrow 3 \text{ favourable}\)

\(P(\text{even}) = \frac{3}{6}\)

A bag contains 3 red, 2 blue and 5 green marbles. One marble is chosen. Find \(P(\text{red})\) as a decimal.

\(\text{Total marbles} = 3 + 2 + 5 = 10\)

\(P(\text{red}) = \frac{3}{10}\)

The probability of rain tomorrow is \(0.3\). What is the probability that it does \(\text{not}\) rain?

  1. \(0.3\)
  2. \(0.7\)
  3. \(0.5\)
  4. \(1.3\)

Answer: \(0.7\)

\(P(\text{not } A) = 1 - P(A)\)

\(P(\text{no rain}) = 1 - 0.3\)

A coin is tossed twice. Find the probability of getting \(\text{two heads}\).

\(\text{Tree diagram outcomes: } HH, HT, TH, TT\)

\(\text{Only one outcome is } HH.\)

\(P(HH) = \frac{1}{4}\)

*List all outcomes with a tree diagram before counting favourable ones.