# Free Probability 02 Practice Test - 9th Grade

It is known that a box of 600 electric bulbs contains 12 defective bulbs. One bulb is taken out at random from this box. What is the probability that it is a non-defective bulb?

A.

588600

B.

12600

C.

0.94

D.

0.98

#### SOLUTION

Solution : A and D

Number of non-defective bulbs = 600 – 12 = 588

Total number of bulbs = 600

Probability of picking a non-defective bulb =Number of non-defective bulbsTotal number of bulbs

Probability of picking a non-defective bulb = 588600 = 0.98

If there are 10 apples, 10 oranges and 10 mangoes in a fruit basket, then the probability of not picking a mango is 13.

A.

True

B.

False

#### SOLUTION

Solution : B

Number of mangoes = 10

Total number of fruits = 10 + 10 + 10 = 30

Probability of picking a mango = Number of mangoesTotal number of fruits

Probability of picking a mango = 1030=13

Probability of not picking a mango = 113=23.

If 20 students in a class failed an exam, the probability of a student selected at random getting passed in an exam is 0.6. The number of students in the class is = ___ .

#### SOLUTION

Solution :

Let the number of students in a class be x.

The probability of students passing an exam = 0.6

Number of students who failed an exam = 20

Number of students who passed an exam =x20

Probability of a student passing an exam =Number of students who passed an examsNumber of students in a class

0.6=x20x

0.6x=x20

0.4x=20

x=50

The number of students in the class is 50.

Last week, it rained on 5 days out of 7 days. The probability that if we pick a random day from the week, it will be a rainy day is

A.

57

B.

75

C.

27

D.

77

#### SOLUTION

Solution : A

Given, it had rained 5 out of 7 days.
i.e., Number of rainy days = 5
Total number of days = 7
Then,
Probability =Number of rainy daysTotal number of days=57

An action which results in one or several outcomes is called as a _______.

A. outcome
B. trial
C. sample space
D. none of the above

#### SOLUTION

Solution : B

.

Probability of occurrence of an event is defined as ______.

A.

No. of favourable outcomes / Total number of outcomes

B.

Favourable outcomes X Total number of outcomes.

C.

Total number of outcomes / No. of favourable outcomes

D.

Happening + Not Happening

#### SOLUTION

Solution : A

.

Which of the following is not the outcome when you throw an unbiased die?

A.

Getting a face of 1

B.

Getting a face of 2

C.

A multiple of 7

D.

A multiple of 2

#### SOLUTION

Solution : C

When you throw an unbiased die, the outcomes are 1, 2, 3, 4, 5 and 6 and none of them are multiple of 7.

It is 82% likely that India will win the match means that, ___.

A.

there is 100% chance that India will win.

B.

there is 18% chance for India to lose the match. So India will definitely not win.

C.

there is 82% chance that India will win. So India will certainly win.

D.

there is 82% chance that India will win but we cannot say that India will definitely win.

#### SOLUTION

Solution : D

It is 82% likely that India will win the match means that there is 82% chance that India is winning the match. There is still 18% uncertainty that India will not win. In terms of probability, the probability of India winning will be 0.82. So India may or may not win. Therefore, we cannot say that India will definitely win.

If we roll a die, there are total six possible outcomes (1,2,3,4,5,6). What is the probability of getting 2?

A. 23
B. 16
C. 12
D. 14

#### SOLUTION

Solution : B

Suppose a die is rolled, the possible outcomes are 1, 2, 3, 4, 5, 6. Each number appearing on the face of a die does not affect the other numbers. Each number has a probability of 16 to occur when a die is rolled. It does not depend on the number that it shows.

For instance, the probability that we roll a die and 2 comes is
16, since there is only single 2 on the cube.

Two kids Goutham and Pavani are fighting for coins. Finally, Goutham won and stole a coin from Pavani's pocket which has four different coins ( a 1 rupee coin, a 2 rupee coin, a 5 rupee coin, a 10 rupee coin). What are the total number of possible outcomes when Goutham tried to steal a coin?

A.

4

B.

5

C.

2

D.

1

#### SOLUTION

Solution : A

As there are four different coins in Pavani's pocket, so there are 4 possible ways in which Goutham can steal a coin i.e. 1 rupee coin, 2 rupee coin, 5 rupee coin, 10 rupee coin. Therefore a total number of possible outcomes are 4.