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Experimental Probability

Experimental probability is the probability found from actual trials by dividing the number of times an event occurs by the total number of trials.

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Student-friendly explanation

This probability comes from observed data. It may change when the experiment is repeated more times, especially when the number of trials is small.

How to write this in exams

  1. 1

    Start with the exact idea

    Experimental probability is the probability found from actual trials by dividing the number of times an event occurs by the total number of trials.

  2. 2

    Then show how to use it

    Find the event count, find total trials, write event count over total trials, and simplify if required.

  3. 3

    Add one concrete example

    If a coin is tossed 50 times and heads appears 28 times, the experimental probability of heads is 28/50.

  4. 4

    Avoid this incomplete answer

    Using 1/4 for red only because a spinner has four colours is wrong when the question asks for observed experimental probability.

Definition

Experimental probability is the probability found from actual trials by dividing the number of times an event occurs by the total number of trials.

Example

If a coin is tossed 50 times and heads appears 28 times, the experimental probability of heads is 28/50.

Rule to remember

Experimental probability = number of times the event occurs / total number of trials.

Memory hook

Experimental means evidence from trials, not only equal-looking possibilities.

Examples and method

Worked example

A spinner is spun 60 times and lands on red 18 times. Experimental probability of red = 18/60 = 3/10.

Method to apply

Find the event count, find total trials, write event count over total trials, and simplify if required.

Diagram support

A frequency table can be used to show outcomes and their observed counts.

How CBSE asks it

Questions usually give a table of observed results and ask for probability based on that record.

Avoid common mistakes

Common confusion

Students often use the theoretical answer 1/2 even when the question gives actual trial results.

Common wrong answer

Using 1/4 for red only because a spinner has four colours is wrong when the question asks for observed experimental probability.

Exam tip

If the question says observed, recorded, surveyed, tossed many times, or experiment result, use the given data.

Quick check

A die is thrown 40 times and 6 appears 7 times. What is the experimental probability of getting 6?

The experimental probability of getting 6 is 7/40 because 6 appeared 7 times out of 40 actual trials.

Answer writing and exam use

1-mark answer

Experimental probability is the probability found from actual trials by dividing the number of times an event occurs by the total number of trials.

2-mark answer

Experimental probability is the probability found from actual trials by dividing the number of times an event occurs by the total number of trials. Experimental probability = number of times the event occurs / total number of trials. If a coin is tossed 50 times and heads appears 28 times, the experimental probability of heads is 28/50.

3-mark answer

This probability comes from observed data. It may change when the experiment is repeated more times, especially when the number of trials is small. Experimental probability = number of times the event occurs / total number of trials. A spinner is spun 60 times and lands on red 18 times. Experimental probability of red = 18/60 = 3/10. Questions usually give a table of observed results and ask for probability based on that record. Using 1/4 for red only because a spinner has four colours is wrong when the question asks for observed experimental probability.
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