Free Maths Calculator

Probability Calculator

Work out probabilities as fractions first, the way exams want them: one event, two independent events happening together, either of two events that cannot both happen, or the full tree for two events. Every answer is simplified and shown as a fraction, a decimal and a percentage.

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    Worked Example

    A fair six-sided dice is rolled. What is the probability of rolling more than 4?

    1. Count the ways: 5 and 6, so 2 ways out of 6 outcomes
    2. P = 2/6, which simplifies to 1/3
    3. As a decimal 0.3333, as a percentage 33.33%

    Answer: 1/3

    Try These Yourself

    A coin is flipped and a dice is rolled. P(heads AND a six)?Show answerHide answer

    Answer: 1/12

    Independent events: 1/2 × 1/6.

    A bag has P(red) = 3/10 and P(blue) = 2/10. P(red or blue)?Show answerHide answer

    Answer: 1/2

    Cannot both happen: 3/10 + 2/10 = 5/10.

    P(rain tomorrow) = 0.3. What is P(no rain)?Show answerHide answer

    Answer: 0.7

    Certain something happens: 1 − 0.3.