Probability - Quantitative Aptitude (MCQ) questions

1)   Three unbiased coins are tossed. What is the probability of getting at least 2 tails?
- Published on 06 Jul 15

a. 0.75
b. 0.5
c. 0.25
d. 0.2
Answer  Explanation 

ANSWER: 0.5

Explanation:
S = {HHH, HHT, HTH, HTT, THH, THT, TTH, TTT}
E = {HTT, THT, TTH, TTT}
n(S) = 8
n(E) = 4
P(E) =n(E) / n(S) = 4/8 = 0.5


2)   Two friends A and B apply for a job in the same company. The chances of A getting selected is 2/5 and that of B is 4/7. What is the probability that both of them get selected?
- Published on 06 Jul 15

a. 8/35
b. 34/35
c. 27/35
d. None of these
Answer  Explanation 

ANSWER: 8/35

Explanation:
P(A) = 2/5
P(B) = 4/7
E = {A and B both get selected}
P(E) = P(A)*P(B)
= 2/5 * 4/7
= 8/35


3)   Tickets numbered 1 to 50 are mixed and one ticket is drawn at random. Find the probability that the ticket drawn has a number which is a multiple of 4 or 7?
- Published on 06 Jul 15

a. 9/25
b. 9/50
c. 18/25
d. None of these
Answer  Explanation 

ANSWER: 9/25

Explanation:
S = {1, 2, 3, … , 49, 50}
E = {4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 7, 14, 21, 35, 42, 49}
n(S) = 50
n(E) = 18
P(E) = n(E)/n(S) = 18/50
= 9/25


4)   Two dice are tossed simultaneously. Find the probability that the total is a prime number.
- Published on 15 Jun 15

a. 7/9
b. 5/12
c. 1/6
d. 5/9
Answer  Explanation 

ANSWER: 5/9

Explanation:
No explanation is available for this question!


5)   A class consists of 15 girls and 10 boys. Three students are to be randomly selected. Find the probability that one boy and two girls are picked.
- Published on 15 Jun 15

a. 1/50
b. 3/25
c. 21/46
d. 25/122
Answer  Explanation 

ANSWER: 21/46

Explanation:
No explanation is available for this question!


6)   A dice is rolled twice. What is the probability of getting sum 9?
- Published on 12 Jun 15

a. 2/3
b. 1/3
c. 1/9
d. 3/9
Answer  Explanation 

ANSWER: 1/9

Explanation:
Possible event = 6*6 = 36

Favourable outcomes= {(3, 6), {4, 5}, {5, 4}, (6, 3)}

Thus probability; favourable/total
= 4/36

=> 1/9


7)   A box has 10 black and 10 white balls. What is the probability of getting two balls of the same color?
- Published on 12 Jun 15

a. 10/19
b. 9/38
c. 9/19
d. 5/38
Answer  Explanation 

ANSWER: 9/19

Explanation:
No explanation is available for this question!


8)   Three coins are tossed. What is the probability of getting at most two tails?
- Published on 19 Oct 15

a. 7/8
b. 1/8
c. 2/8
d. 4/8
Answer  Explanation 

ANSWER: 7/8

Explanation:
It is given that 3 coins are tossed simultaneously.

=>Total outcomes when one coin is tossed=2

=>Total outcomes when 3 coins are tossed= 2n = 2 X 2 X 2

=8 outcomes

Favourable outcomes: TTH, THT, HTT, THH, THT,HHT,HHH=7

Therefore, Probability= 7/8


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