4
Q:

Out of 3 girls and 6 boys a group of three members is to be formed in such a way that at least one member is a girl. In how many different ways can it be done?

A) 64 B) 84
C) 56 D) 20

Answer:   A) 64



Explanation:

Total number of possible ways = 9C3 = 84 ways

Required atleast one girl in the group of three = total possible ways - ways in which none is girl

None of the members in the group is girl = 6C3 = 20

 

Therefore, number of ways that at least one member is a girl in the group of three

= 84 - 20

= 64 ways.

Q:

There are 26 balls marked with alphabetical order A to Z. What is the probability of selecting vowels listed balls? 

A) 1 B) 21/26
C) 5/26 D) 5
 
Answer & Explanation Answer: C) 5/26

Explanation:

We know that,

Total number of balls n(S) = 26

Number of vowels n(E) = 5

Hence, required probability = n(E)/n(S) = 5/26.

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5 227
Q:

A group of five persons is formed from five boys and four girls. Find the probability that there are at least two girls in the group?

A) 110/129 B) 5/6
C) 121/126 D) 3/7
 
Answer & Explanation Answer: A) 110/129

Explanation:

Total number of possible ways = 

9C5 = 9 x 8 x 7 x 6 x 55 x 4 x 3 x 2 x 1 = 126

Number of favorable cases = 

4C2 x 5C3 + 4C3 x 5C2 + 4C4 x 5C14 x 32 x 1 x 5 x 4 x 33 x 2 x 1 + 4 x 3 x 23 x 2 x 1 x 5 x 4 2 x 1 + 1 x 5= 6 x 10 + 4 x 10 + 5= 60 + 40 + 5= 105

 

Therefore, required probability = 105/126 = 5/6

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2 329
Q:

A bag contains 5 red smileys, 6 yellow smileys and 3 green smileys. If two smileys are picked at random, what is the probability that both are red or both are green in colour?

A) 7 B) 1/7
C) 3/7 D) 0
 
Answer & Explanation Answer: B) 1/7

Explanation:

Given total number of smileys = 5 + 6 + 3 = 14

Now, required probability = 

5C214C2 + 3C214C2 = 1091 + 391 = 1391 = 17

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1 376
Q:

When two dice are thrown simultaneously, what is the probability that the sum of the two numbers that turn up is less than 12?

A) 35/36 B) 17/36
C) 15/36 D) 1/36
 
Answer & Explanation Answer: A) 35/36

Explanation:

When two dice are thrown simultaneously, the probability is n(S) = 6x6 = 36

dice_thrown_simulataneously1532668754.png image

Required, the sum of the two numbers that turn up is less than 12

That can be done as n(E)

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

= 35

Hence, required probability = n(E)/n(S) = 35/36.

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6 868
Q:

In a purse there are 30 coins, twenty one-rupee and remaining 50-paise coins. Eleven coins are picked simultaneously at random and are placed in a box. If a coin is now picked from the box, find the probability of it being a rupee coin?

A) 4/7 B) 2/3
C) 1/2 D) 5/6
 
Answer & Explanation Answer: B) 2/3

Explanation:

Total coins 30

In that,

1 rupee coins 20

50 paise coins 10

Probability of total 1 rupee coins =  20C11

Probability that 11 coins are picked = 30C11

Required probability of a coin now picked from the box is 1 rupee = 20C11/30C11 = 2/3.

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10 1581
Q:

In a box, there are 9 blue, 6 white and some black stones. A stone is randomly selected and the probability that the stone is black is ¼. Find the total number of stones in the box? 

A) 15 B) 18
C) 20 D) 24
 
Answer & Explanation Answer: C) 20

Explanation:

We know that, Total probability = 1

Given probability of black stones = 1/4

=> Probability of blue and white stones = 1 - 1/4 = 3/4

But, given blue + white stones =  9 + 6 = 15

Hence,

3/4 ----- 15

 1   -----  ?

=> 15 x 4/3 = 20.

 

Hence, total number of stones in the box = 20.

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12 1497
Q:

What is the probability of an impossible event?

A) 0 B) -1
C) 0.1 D) 1
 
Answer & Explanation Answer: A) 0

Explanation:

The probability of an impossible event is 0.

The event is known ahead of time to be not possible, therefore by definition in mathematics, the probability is defined to be 0 which means it can never happen.

 

The probability of a certain event is 1.

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15 1867
Q:

In a box, there are four marbles of white color and five marbles of black color. Two marbles are chosen randomly. What is the probability that both are of the same color?

A) 2/9 B) 5/9
C) 4/9 D) 0
 
Answer & Explanation Answer: C) 4/9

Explanation:

Number of white marbles = 4

Number of Black marbles = 5

Total number of marbles = 9

Number of ways, two marbles picked randomly = 9C2

Now, the required probability of picked marbles are to be of same color = 4C2/9C2  +  5C2/9C2

= 1/6 + 5/18

= 4/9.

 

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