Chapter 7
The Mathematics of Maybe: Introduction to Probability
CBSE Class 9
Mathematics Solutions
Educart Mathematics class Class 9 NCERT Exemplar cover
Question:

Write the sample space and calculate the probability based on the given information.

(A) Two coins are tossed at the same time. What is the probability of getting at least one head?

(B) Ten identical cards numbered 1 to 10 are placed in a box. One card is drawn at random. What is the probability of drawing a card with an even number?

(C) A die is rolled once. What is the probability of getting a number greater than 4?

(D) A bag contains 3 red balls, 2 blue balls, and 1 green ball. One ball is picked at random. What is the probability that it is not red?

(E) Three coins are tossed simultaneously. What is the probability of getting exactly two heads?

Answer: Verified

(A) Sample space S={HH,HT,TH,TT}S = \{HH, HT, TH, TT\}, n(S)=4n(S) = 4.

Event 'at least one head' = {HH, HT, TH}, so n(E) = 3.

P(at least one head)=34P(\text{at least one head}) = \frac{3}{4}

(B) S = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, n(S) = 10.

Even numbers = {2, 4, 6, 8, 10}, n(E) = 5.

P(even)=510=12P(\text{even}) = \frac{5}{10} = \frac{1}{2}

(C) S = {1, 2, 3, 4, 5, 6}.

Numbers greater than 4 = {5, 6}, n(E) = 2.

P(number greater than 4)=26=13P(\text{number greater than 4}) = \frac{2}{6} = \frac{1}{3}

(D) Total balls = 6.

Non-red balls = 2 + 1 = 3.

P(not red)=36=12P(\text{not red}) = \frac{3}{6} = \frac{1}{2}

(E) Sample space S = {HHH, HHT, HTH, HTT, THH, THT, TTH, TTT}, n(S) = 8.

Exactly two heads: {HHT, HTH, THH}, n(E) = 3.

P(exactly two heads)=38P(\text{exactly two heads}) = \frac{3}{8}

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