# Probability Class 9

Probability class 9 – In an experiment an is the collection of all the possible outcomes during the the experiment. 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.

For example: 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 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.

### Probability class 9 Examples

#### Practise This Question

The radii of two cylinders are in the ratio of 2:3 and their heights are in the ratio of 5:3. The ratio of their volumes is: