Page 273 - ICSE Math 8

EXERCISE

1. Two fair coins are tossed 200 times. Two heads are obtained 120 times. Now, if the coin is tossed at
random, what is the probability of getting 2 heads?
2. Two fair coins are tossed simultaneously. Find the probability of getting:
(a) 2 tails. (b) no head. (c) no tail.
(d) same face on each coin. (e) different faces on the coins.
3. Two dice are rolled simultaneously. Find the probability of getting:
(a) an odd number on both dice. (b) sum of numbers as a multiple of 2.
(c) sum of numbers as prime number. (d) not a doublet.
(e) difference of digits as 2. (f) sum of numbers as at least 10.
4. What is the probability that a number selected from the numbers 1, 2, 3, ..., 16 is a prime number?
5. A bag contains 6 red and 8 white balls. One ball is drawn at random. What is the probability that the ball
drawn is white?
6. An urn contains 3 red, 5 blue, 4 green and 6 orange marbles. A marble is drawn from the urn at random.
What is the probability that it is:
(a) a green marble? (b) not a red marble?
(c) either blue or orange marble? (d) an orange marble?
7. A survey of 200 families in a society shows the following results:

Number of cars owned by a family 0 1 2 3 or more

Number of families 20 105 60 15
Out of these families, one is chosen at random. What is the probability that the chosen family has:
(a) no car? (b) 2 cars? (c) more than 1 car? (d) 3 or more cars?
8. A bag contains 4 white and 5 blue balls. They are mixed thoroughly and one ball is drawn at random.
What is the probability of getting (a) a white ball? (b) a blue ball?
9. In a lottery, there are 10 prizes and 20 blanks. A ticket is chosen at random. What is the probability of
getting a prize?
10. It is known that a box of 100 electric bulbs contains 8 defective bulbs. One bulb is taken out at random
from the box. What is the probability that the bulb drawn is (a) defective? (b) non-defective?
AT A GLANCE

¾ An experiment in which all possible outcomes are known but the exact outcome cannot be predicted in
advance is known as random experiment.
¾ An event is one or more outcomes of a random experiment.
¾ Performing a random experiment is called a trial.
¾ The outcomes of an event are said to be equally likely if they have equal chances of occurring.

¾ A collection of all possible outcomes of a random experiment is called sample space.
¾ If there are n outcomes associated to a random experiment such that m of them are favourable to
Number of outcomes favourable to event A
an event A, then probability of happening of A, i.e., P(A) = Total numberof possibleouttcomes .

m
\ P(A) = n
¾ For any event A, P(A) + P( A ) = 1.

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