Probability Class 9 Notes - Chapter 15

Probability Class 9 notes are provided here to help students understand the concept of this topic more effectively. We can define probability as the measure of the likelihood that an event will occur. We can calculate the probability of a single event occurring by dividing the number of events by the number of possible outcomes. Also, learn probability and statistics here.

Probability Definition

Probability is basically the chances of an event to occur. The probability P(E) of an event E is determined by:

P(E) = \(\frac{Number \;of\; trials\; in\; which \;E\; has\; happened }{Total\; number\; of \;trials}\)

The Probability of any event always lies between 1 and 0.

Example of Probability

A coin is tossed 100 times resulting in the following frequencies: Heads 45 times and Tail 55 times. For calculating the probability of all possible events let us assume ‘H’ as an event of getting a head and ‘T’ as an event of getting a tail. Then, the probability of getting heads:

P (H) = \(\frac{Number \;of\; Heads }{Total\; number\; of \;trials}\;=\;\frac{45}{100}\;=\;0.45\)

Similarly, the probability of getting a tail:

P (T) = \(\frac{Number \;of\; Tail }{Total\; number\; of \;trials}\;=\;\frac{55}{100}\;=\;0.55\)

In the above example, the probability of getting tail P(T) + probability of getting heads P(H) = 0.45 + 0.55 = 1. Also, there are only 2 possible outcomes in each trial i.e. either heads or tails.

Important Questions

Q.1) A coin is tossed 1000 times with the following frequencies:
Tail: 545, and Head: 455. Calculate the probability for each event.

Q.2) A die is thrown 1000 times with the frequencies for the outcomes 1, 2, 3,
4, 5 and 6 as given in the table below:

Outcome 1 2 3 4 5 6
Frequency 179 150 157 149 175 190

Find the probability of getting each outcome.

Q.3) The percentage of marks obtained by a student in the monthly unit tests
are mentioned in the table below:

Test 1 2 3 4 5
Marks 78 76 89 90 81

Find the probability that the student gets more than 80% marks in a unit test based on the given data.

Stay tuned with BYJU’S and get detailed notes of all concepts of Class 9 mathematics.

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