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Probability Quiz for IBPS

IBPS EXAM Guru
1. What is the probability that a card drawn at random from a pack of 52 cards is either a king or a
spade?
1) 17/52  2) 4/13  3) 3/13  4) 13/52  5) None of these
Solution:(2)
Required probability =3/52 + 13/52 = 16/52 = 4/13
(Note : why 13/52 because there are 13 spades and why 3/52 instead of 4/52 (there are four
kings)because one king is already counted in spades)

2. If three unbiased coins are tossed simultaneously, then the probability of exactly two heads, is
1) 1/8  2) 2/8  3) 3/8  4) 4/8  5) none of the above
Solution: (3).
n(S) = 23 =8
Let E = event of getting exactly two heads
={ (H,H,T), (H,T,H), (T,H,H) }
= n(E) = 3
Therefore Required probability =3/8

3. When two dice are rolled, what is the probability that the sum of the numbers appeared on them is
11?
1) 1/6  2) 1/18  3) 1/9  4) 1  5) none of the above
Solution: (2) .
n(S) =36
n(E) = {(5,6),(6,5)} =2
Therefore P(E) = n(E) / n(S) = 2/36 = 1/18

4. A basket contains three blue and four red balls. If three balls are drawn at random from the basket,
what is the probability that all the three balls are either blue or red?
1) 1  2) 1/7  3) 3/14  4) 3/28  5) None of the above
Solution: (2)
Probability to be a blue = 3 C3 / 7 C3 47
Therefore Required Probability = 3C3 / 7C3 = 4 C3 / 7C3 = 5/35 = 1/7

5. A number is selected at random from the set { 1,2,3,…………………,50}. The probability that it is a
prime, is
1) 0.1  2) 0.2  3) 0.3  4) 0.7  5) None of the above
Solution:(3)
n (S) =50
Prime numbers are = 2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
Therefore n(E)=15
P(E) = 15/50 = 3/10 =0.3

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