myhelper: RD Sharma 2020 solution class 9 chapter 25 Probabilty FBQS

RD Sharma 2020 solution class 9 chapter 25 Probabilty FBQS

FBQS

Page-25.17

Question 1:

Fill In The Blanks

If an experiment does not produce the same outcomes every time but the outcomes in a trial is one of the several possible outcomes, then it is called an ________ experiment.

Answer 1:

If an experiment does not produce the same outcomes every time but the outcomes in a trial is one of the several possible outcomes, then it is called an __random__ experiment.

Question 2:

Fill In The Blanks

An outcome of a trial of a random experiment is called an _________ event.

Answer 2:

An outcome of a trial of a random experiment is called an __elementary__ event.

Question 3:

Fill In The Blanks

A collection of two or more possible outcomes (elementary events) of a trial is called a ________ event.

Answer 3:

A collection of two or more possible outcomes (elementary events) of a trial is called a __compound__ event.

Question 4:

Fill In The Blanks

In a sample study of 642 people, it was found that 514 people have a high school certificate. If a person is selected at random, the probability, that the person has a high school certificate is _______.

Answer 4:

Number of people in the sample study = 642

Number of people having high school certificate = 514

∴ P(Person selected at random has a high school certificate)

=

\frac{Number of people having high school certificate}{Number of people in the sample study}

\frac{514}{642}

\frac{257}{321}

Thus, the probability that the person selected at random has a high school certificate is

\frac{257}{321}

.

In a sample study of 642 people, it was found that 514 people have a high school certificate. If a person is selected at random, the probability, that the person has a high school certificate is

\frac{257}{321}

Question 5:

Fill In The Blanks

80 bulbs are selected at random from a lot and their life time (in hrs) is recorded in the form of following frequency table:

Life time (in hrs): 300 500 700 900 1000
Frequency : 10 12 23 25 10

One bulb is selected at random from the lot. The probability that its life is 1150 hours is __________.

Answer 5:

Number of bulbs in the lot = 80

Number of bulbs having life time 1150 hours = 0

∴ P(Bulb selected at random has life time 1150 hours)

=

\frac{Number of bulbs having life time 1150 hours}{Number of bulbs in the lot}

\frac{0}{80}

= 0

Thus, the probability that a bulb selected at random from the lot has life time 1150 hours is 0.

One bulb is selected at random from the lot. The probability that its life is 1150 hours is ____0____.

Question 6:

Fill In The Blanks

In a survey of 364 children aged 19-36 months, it was found that 91 liked to eat patato chips. If a child is selected at random, the probability that he/she does not like eat patato chips, is _________.

Answer 6:

Number of children in the survey = 364

Number of children who liked to eat potato chips = 91

∴ Number of children who did not liked to eat potato chips

= Number of children in the survey − Number of children who liked to eat potato chips

= 364 − 91

= 273

Now,

P(A child selected at random does not like to eat potato chips)

=

\frac{Number of children who did not liked to eat potato chips}{Number of children in the survey}

\frac{273}{364}

\frac{3}{4}

Thus, the probability that a child selected at random does not like to eat potato chips is

\frac{3}{4}

.

In a survey of 364 children aged 19-36 months, it was found that 91 liked to eat potato chips. If a child is selected at random, the probability that he/she does not like eat potato chips, is

\frac{3}{4}

Question 7:

Fill In The Blanks

In Q.No. 5, the probability that a bulb selected at random from the the lot has life less than 900 hours is _________.

Answer 7:

Number of bulbs in the lot = 80

Number of bulbs having life time less than 900 hours

= Number of bulbs having life time 300 hours + Number of bulbs having life time 500 hours + Number of bulbs having life time 700 hours

= 10 + 12 + 23

= 45

∴ P(Bulb selected at random has life time less than 900 hours)

=

\frac{Number of bulbs having life time less than 900 hours}{Number of bulbs in the lot}

\frac{45}{80}

\frac{9}{16}

Thus, the probability that a bulb selected at random from the lot has life time less than 900 hours is

\frac{9}{16}

.

The probability that a bulb selected at random from the the lot has life less than 900 hours is

\frac{9}{16}

Question 8:

Fill In The Blanks

Two coins are tossed 1000 times and outcomes are recorded as below:

Numbers of heads: 2 1 0
Frequency: 200 550 250

The probability of getting at most one head is _______.

Answer 8:

Two coins are tossed 1000 times.

∴ Total number of trials = 1000

Let E be the event of getting at most one head on the two coins.

Number of trials for getting at most one head

= Frequency of getting 0 heads + Frequency of getting 1 head

= 250 + 550

= 800

∴ Probability of getting at most one head = P(E) =

\frac{Number of trials for getting at most one head}{Total number of trials} = \frac{800}{1000} = \frac{4}{5}

Thus, the probability of getting at most one head is

\frac{4}{5}

.

The probability of getting at most one head is

\frac{4}{5}

Page-25.18

Question 9:

Fill In The Blanks

In a medical examination of students of a class, the following blood groups are recorded:

Blood group: A AB B O
Number of students: 10 13 12 5

A student is selected at random from the class. The probability that he/she has blood group B, is __________.

Answer 9:

Total number of students in the class = 10 + 13 + 12 + 5 = 40

Number of students having blood group B = 12

∴ P(A student selected at random has blood group B)

= $\frac{Number of students having blood group B}{Total number of students in the class}$

= $\frac{12}{40}$

= $\frac{3}{10}$

Thus, the probability that a student selected at random from the class has blood group B is $\frac{3}{10}$ .

A student is selected at random from the class. The probability that he/she has blood group B, is $\frac{3}{10}$ .

Question 10:

Fill In The Blanks

A die is thrown 1000 times and the outcomes were recorded as follows:

Outcomes: 1 2 3 4 5 6
Frequency: 180 150 160 170 150 190

If the die is thown once more, then the probability that its show 5 is _________.

Answer 10:

It is given that a die is thrown 1000 times.

∴ Total number of trials = 1000

Let E be the event that the die shows 5.

Number of trials of getting 5 on the die = Frequency of getting 5 on the die = 150

∴ P(Die shows the number 5) = P(E) = $\frac{Number of trials of getting 5 on the die}{Total number of trials} = \frac{150}{1000} = \frac{3}{20}$

Thus, the probability that die shows 5 is $\frac{3}{20}$ .

If the die is thrown once more, then the probability that its show 5 is $\frac{3}{20}$ .