Probability Quiz Set 003 | Maths Aptitude Quiz Questions and Mock Test on Probability Set 3 | mock tests for Bank PO, SSC Exams, SO Clerical Exam, GATE Exam, LIC AO, GIC AO, etc.

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Question 1

A box contains 8 khaki, 2 sky blue and 7 navy marbles. What is the probability of drawing a navy marble if 2 marbles are drawn out randomly?

${91/136}$.

$7/17$.

$92/136$.

$96/136$.

Soln.
Ans: a

Total number of marbles is 17. Combinations of 2 marbles that are possible = ¹⁷C₂ = ${17 × 16}/2$ = 136. If one of the two balls is navy, then both balls will be navy in ⁷C₂ = ${7 × (7 - 1)}/2$ = 21 ways. The number of ways in which non-navy can be drawn out are 7 × (8 + 2). So total favorable outcomes = 21 + 7 × 10 = 91, and the probability is 91/136 = ${91/136}$.

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Question 2

From a deck of 52 cards 1 card is drawn at random. What is the probability that it will be a red "5"?

${1/26}$.

$5/7$.

$2/26$.

$6/26$.

Soln.
Ans: a

Number of ways of drawing 1 card = 52. There are two red "5" in the whole pack. So favorable chances are 2. Probability = 2/52 = 1/26.

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Question 3

Three unbiased coins are tossed. What is the probability of getting at most two heads?

7/8.

3/8.

1/8.

5/8.

Soln.
Ans: a

Three coins will give 8 possibilities = 2 × 2 × 2. At most two heads means 1 or 2 heads. We will not get this only when all tails come, which is possible only once. So 8 - 1 = 7 chances are favorable. The probability = 7/8.

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Question 4

A box contains 3 navy, 4 green and 5 khaki marbles. What is the probability of drawing a marble that is not khaki if 2 marbles are drawn out randomly?

${7/22}$.

$5/12$.

$8/66$.

$12/66$.

Soln.
Ans: a

Total number of marbles is 12. Combinations of 2 marbles that are possible = ¹²C₂ = ${12 × 11}/2$ = 66. Chances of drawing a non-khaki ball are ⁷C₂ = $(7 × (7 - 1))/2$ = 21. So probability = 21/66 = ${7/22}$.

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