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Problems on Probability

Probability - Aptitude

1.In a throw of a coin, find the probability of getting a head.

A. 1✘

B. 3/4✘

C. 1/4✘

D. 1/2✔

x

 

Option: D

Explanation

S = {H, T}

E = {H}

P(E) = n(E)/n(S) = 1/2

✉ Answer


2.Two unbiased coins are tossed. What is the probability of getting at most one head?

A. 3/4✔

B. 1/4✘

C. 1✘

D. 3✘

x

 

Option: A

Explanation

S = {HH, HT, TH, TT}

E = event of getting at most head

E = {HH, HT, TH}

P(E) = n(E)/n(S) = 3/4

✉ Answer


3.An unbiased die is tossed. Find the probability of getting a multiple of 3.

A. 1/4✘

B. 3/4✘

C. 2/3✘

D. 1/3✔

x

 

Option: D

Explanation

S = {1, 2, 3, 4, 5, 6}

E = event of getting multiple of 3

E = {3, 6}

P(E) = n(E)/n(S) = 2/6 = 1/3

✉ Answer


4.In a simultaneous throw of a pair of dice, find the probability of getting a total more than 7.

A. 5/12✔

B. 7/12✘

C. 11/12✘

D. 1/12✘

x

 

Option: A

Explanation

n(S) = {6 * 6} = 36

E = event of getting a total more than 7

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

P(E) = n(E)/n(S) = 15/36 = 5/12

✉ Answer


5.A bag contains 6 white and 4 black balls. Two balls are drawn at random. Find the probability that they are of the same colour.

A. 7/15✔

B. 2/15✘

C. 1/15✘

D. 14/15✘

x

 

Option: A

Explanation

n(S) = number of ways of drawing 2 balls out of (6 + 4) = 10C2

n(S) = (10 * 9)/(2 * 1) = 45

E = event of getting both balls of the same colour

n(E) = number of ways of drawing (2 balls out of 6) or (2 balls out of 4)

n(E) = (6C2 + 4C2) = ((6 * 5)/(2 * 1)) + ((4 * 3)/(2 * 1)) = 15 + 6 = 21

P(E) = n(E)/n(S) = 21/45 = 7/15

✉ Answer


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