Page 267 - ICSE Math 7

7
Out of 10 trials, head appears 7 times. The experimental probability of head is , which is nowhere
1 10
near the theoretical probability of head which is . This anomaly is due to the fact that experimental
2
probability comes closer and closer to theoretical probability only in the long run, i.e., more the number
of trials, the better is the estimate of experimental probability.
Conduct an activity of tossing a coin 100 times and observe the number of heads. You will observe
1
the probability of head is nearer to . Ask your friends to toss a coin 100 times each. What are their
2
probabilities? Collect the data of all your friends and find the probability of head if the coin is tossed
200 times, 300 times, 400 times, ..., and so on. You will agree to the fact that as the number of trials
1
increases, the experimental probability of head comes closer and closer to .
2

EXERCISE

1. Describe the chances of occurrence of the following events using the words: impossible,
not likely, equally likely, most likely or certain.
(a) A red marble picked up at random from a bag containing 8 red marbles and 2 black marbles.
(b) The chances of getting tail in a toss of a coin once.

(c) The chances of India cricket team to win a toss.
(d) You will grow over 100 feet tall.
(e) A year having 12 months.
(f) All 10 traffic signal lights enroute to school will be green.
2. Find the probabilities of the following.
(a) February always having 29 days (b) A month having 31 days
(c) A blue ball drawn from 15 blue balls (d) The sum of two odd numbers is even

(e) Drawing a red card from a well-shuffled deck of playing cards
(f) Getting an odd number when a die is thrown once
3. A box contains 3 red balls, 7 black balls and 5 green balls. One ball is drawn from the box at

random. Find the probability of drawing a:
(a) green ball. (b) black or red ball. (c) ball that is not black.
4. A coin is tossed twice.

(a) List the outcomes of the sample space.
(b) List the outcomes of the event of getting at least one tail.
(c) List the outcomes of getting exactly one head.

(d) Write probabilities of the event described in parts (b) and (c) above.
5. If one letter is chosen at random from the word “MATHEMATICS”, find the probability of:
(a) choosing M (b) choosing A (c) choosing S (d) choosing a vowel

6. A card is drawn from a well-shuffled deck of 52 cards. Find the probabilities of each of the
following events.
(a) Drawing a black card (b) Drawing a king (c) Not drawing a spade

(d) Drawing an ace (e) Drawing an ace of spade

253