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Class 9 RD Sharma Solutions- Chapter 25 Probability – Exercise 25.1 | Set 1
• Last Updated : 19 Jan, 2021

### Compute the probability of each event.

Solution:

According to the given question,

Coin is tossed 1000 times, that means number of trials are 1000

Let us assume that, event of getting head and event

of getting tail be H and T respectively.

Number of trials in which the H happens = 455

Probability of H = (Number of heads) / (Total number of trials)

P(H) = 455/1000 = 0.455

Similarly,

Number of trials in which the T happens = 545

Probability of T = (Number of trials) / (Total number of trials)

Probability of the event getting a tail, P(T) = 545/1000 = 0.545

### Find the probability of occurrence of each of these events.

Solution:

According to the formula,

Probability of any event = (Number of favorable outcome) / (Total number of trials)

Total number of trials = 95 + 290 + 115 = 500          -(given)

P(Getting two heads) = 95/500 = 0.19

P(Getting one tail) = 290/500 = 0.58

P(Getting no head) = 115/500 = 0.23

### (v) Getting more tails than heads

Solution:

According to the formula,

Probability of an event = (Number of Favorable outcomes) / (Total Numbers of outcomes)

Given: Total numbers of outcomes = 100

(i) Probability of 2 Heads coming up = 36/100 = 0.36

(ii) Probability of 3 Heads coming up = 12/100 = 0.12

(iii) Probability of at least one head coming up = (38+36+12) / 100 = 86/100 = 0.86

(iv) Probability of getting more Heads than Tails = (36+12)/100 = 48/100 = 0.48

(v) Probability of getting more tails than heads = (14+38) / 100 = 52/100 = 0.52

### (v) More girls than boys

Solution:

According to the formula,

Probability of an event = (Number of Favorable outcomes) / (Total Numbers of outcomes)

Total numbers of outcomes = 211 + 814 + 475 = 1500

(Here, we are assuming that total numbers of outcomes = total number of families)

(i) Probability of having no girl = 211/1500 = 0.1406

(ii) Probability of having 1 girl = 814/1500 = 0.5426

(iii) Probability of having 2 girls = 475/1500 = 0.3166

(iv) Probability of having at the most one girl = (211+814) /1500 = 1025/1500 = 0.6833

(v) Probability of having more girls than boys = 475/1500 = 0.31

### (ii) He does not hit a boundary.

Solution:

Total number of balls played by a player = 30          -(According to the question)

Number of times he hits a boundary = 6

Number of times he does not hit a boundary = 30 – 6 = 24

According to the formula,

Probability of an event = (Number of Favorable outcomes) / (Total Numbers of outcomes)

(i) Probability (he hits boundary) = (Number of times he hit a boundary) / (Total number of balls he played)

= 6/30 = 1/5

(ii) Probability that the batsman does not hit a boundary = 24/30 = 4/5

### (iii) A distinction

Solution:

Total number of unit tests taken = 5

According to the formula,

Probability of an event = (Number of Favorable outcomes) / (Total Numbers of outcomes)

(i) Number of times student got more than 70% = 3

Probability (Getting more than 70%) = 3/5 = 0.6

(ii) Number of times student got less than 70% = 2

Probability (Getting less than 70%) = 2/5 = 0.4

(iii) Number of times student got a distinction = 1

[Marks more than 75%]

Probability (Getting a distinction) = 1/5 = 0.2

### (ii) Does not like it.

Solution:

Total number of students = 200

Students like mathematics = 135

Students dislike Mathematics = 65

According to the formula,

Probability of an event = (Number of Favorable outcomes) / (Total Numbers of outcomes)

(i) Probability (Student likes mathematics) = 135/200 = 0.675

(ii) Probability (Student does not like mathematics) = 65/200 = 0.325

### (i) a (ii) b (iii) ab (iv) o

Solution:

(i) Probability of a student of blood group Favorable outcome A

Total outcome = (Number of Favorable outcomes) / (Total Numbers of outcomes)

= 9/30 = 0.3

(ii) Probability of a student of blood group Favorable outcome B

Total outcome = (Number of Favorable outcomes) / (Total Numbers of outcomes)

= 6/30 = 0.2

(iii) The probability of a student of blood group

Probability of an event = (Number of Favorable outcomes) / (Total Numbers of outcomes)

= 3/30 =0.1

(iv) The probability of a student of blood group

Probability of an event = (Number of Favorable outcomes) / (Total Numbers of outcomes)

= 12/30 = 0.4

### Find the probability that any of these bags chosen at random contains more than 5 kg of flour.

Solution:

Given bag of wheat flour in the question

4.97, 5.05, 5.05, 5.03, 5.00, 5.06, 5.08, 4.98, 5.04, 5.07, 5.00

The total number of wheat flour bags =11.

The number of wheat flour bags contain more than 5 Kg are 7.

Then probability of bags chosen at random =

(The number of wheat flour bags contain more than 5 Kg) / (The total number of wheat flour bags)

= 7/11

### Find the probability that a student was born in August.

Solution:

Probability (Students was born in August) Favorable outcome

Total outcome = (Favorable outcome)/(Total outcome)

= 6/40 = 3/20

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