Probability Basics for Competitive Exam Success

Probability Basics

Q. If a student is selected at random from a group of 20 students, where 12 are girls and 8 are boys, what is the probability that the selected student is a boy?

A. 2/5
B. 1/2
C. 3/5
D. 1/4

Solution

The probability of selecting a boy is the number of boys divided by the total number of students, which is 8/20 = 2/5.

Correct Answer: B — 1/2

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Q. If a student is selected at random from a group of 20 students, where 8 are girls, what is the probability that the selected student is a boy?

A. 3/5
B. 1/4
C. 1/2
D. 2/5

Solution

The number of boys is 20 - 8 = 12. The probability of selecting a boy is 12/20 = 3/5.

Correct Answer: A — 3/5

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Q. In a bag containing 3 red, 2 blue, and 5 green balls, what is the probability of drawing a blue ball?

A. 1/5
B. 1/4
C. 1/10
D. 1/2

Solution

Total balls = 3 + 2 + 5 = 10. Probability of drawing a blue ball = Number of blue balls / Total balls = 2/10 = 1/5.

Correct Answer: B — 1/4

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Q. In a class of 30 students, 18 are boys and 12 are girls. If a student is selected at random, what is the probability that the student is a girl?

A. 2/5
B. 1/3
C. 1/2
D. 3/5

Solution

The probability of selecting a girl is the number of girls divided by the total number of students, which is 12/30 = 2/5.

Correct Answer: A — 2/5

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Q. In a class of 30 students, 18 are boys and 12 are girls. What is the probability of randomly selecting a girl?

A. 2/5
B. 1/3
C. 1/2
D. 3/5

Solution

The probability of selecting a girl is the number of girls divided by the total number of students, which is 12/30 = 2/5.

Correct Answer: A — 2/5

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Q. In a class of 30 students, 18 are girls. If a student is selected at random, what is the probability that the student is a girl?

A. 3/5
B. 2/5
C. 1/2
D. 1/3

Solution

Probability = Number of girls / Total students = 18/30 = 3/5.

Correct Answer: A — 3/5

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Q. In a group of 50 people, 30 like tea, 20 like coffee, and 10 like both. What is the probability that a randomly selected person likes either tea or coffee?

A. 0.4
B. 0.6
C. 0.5
D. 0.7

Solution

Using the principle of inclusion-exclusion, the number of people who like either tea or coffee is 30 + 20 - 10 = 40. The probability is 40/50 = 0.8.

Correct Answer: B — 0.6

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Q. In a lottery, 10 tickets are sold. If you buy 1 ticket, what is the probability of winning?

A. 1/10
B. 1/5
C. 1/2
D. 1/20

Solution

There is 1 winning ticket out of 10. Probability = 1/10.

Correct Answer: A — 1/10

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Q. In a lottery, there are 10 tickets, and 3 of them are winning tickets. If one ticket is drawn at random, what is the probability that it is a winning ticket?

A. 1/10
B. 1/3
C. 3/10
D. 7/10

Solution

The probability of drawing a winning ticket is 3/10.

Correct Answer: C — 3/10

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Q. In a lottery, there are 10 tickets, and 3 of them are winning tickets. What is the probability of selecting a winning ticket?

A. 1/10
B. 3/10
C. 1/3
D. 1/5

Solution

The probability of selecting a winning ticket is the number of winning tickets divided by the total number of tickets, which is 3/10.

Correct Answer: B — 3/10

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Q. In a lottery, there are 10 tickets, of which 2 are winning tickets. What is the probability of selecting a winning ticket?

A. 1/5
B. 1/10
C. 1/2
D. 2/10

Solution

The probability of selecting a winning ticket is the number of winning tickets divided by the total number of tickets, which is 2/10 = 1/5.

Correct Answer: B — 1/10

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Q. In a lottery, there are 10 tickets, of which 3 are winning tickets. What is the probability of selecting a winning ticket?

A. 1/10
B. 1/3
C. 3/10
D. 7/10

Solution

The probability of selecting a winning ticket is the number of winning tickets divided by the total number of tickets, which is 3/10.

Correct Answer: C — 3/10

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Q. In a lottery, there are 100 tickets, and 10 of them are winning tickets. If one ticket is drawn at random, what is the probability that it is a winning ticket?

A. 1/10
B. 1/5
C. 1/20
D. 1/50

Solution

The probability of drawing a winning ticket = Number of winning tickets / Total tickets = 10/100 = 1/10.

Correct Answer: A — 1/10

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Q. In a lottery, there are 100 tickets, and 10 of them are winning tickets. What is the probability of selecting a winning ticket?

A. 1/10
B. 1/5
C. 1/20
D. 1/50

Solution

The probability of selecting a winning ticket is the number of winning tickets divided by the total number of tickets, which is 10/100 = 1/10.

Correct Answer: A — 1/10

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Q. What is the probability of drawing an ace from a standard deck of cards?

A. 1/52
B. 1/13
C. 1/26
D. 1/4

Solution

There are 4 aces in a deck of 52 cards. Therefore, the probability P(ace) = 4/52 = 1/13.

Correct Answer: B — 1/13

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Q. What is the probability of getting a sum of 7 when two dice are rolled?

A. 1/6
B. 1/12
C. 1/36
D. 1/3

Solution

The possible outcomes for a sum of 7 are (1,6), (2,5), (3,4), (4,3), (5,2), (6,1) which gives us 6 favorable outcomes. Total outcomes when rolling two dice = 6 * 6 = 36. Therefore, P(sum of 7) = 6/36 = 1/6.

Correct Answer: A — 1/6

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Q. What is the probability of rolling an even number on a fair six-sided die?

A. 1/6
B. 1/3
C. 1/2
D. 2/3

Solution

Even numbers on a die: 2, 4, 6. Probability = 3/6 = 1/2.

Correct Answer: C — 1/2

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Q. What is the probability of rolling an even number on a single die?

A. 1/2
B. 1/3
C. 1/6
D. 2/3

Solution

Even numbers on a die = 2, 4, 6. Probability = 3/6 = 1/2.

Correct Answer: A — 1/2

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Q. What is the probability of rolling an even number on a single six-sided die?

A. 1/2
B. 1/3
C. 1/6
D. 2/3

Solution

The even numbers on a die are 2, 4, and 6. There are 3 even numbers out of 6 total numbers, so the probability is 3/6 = 1/2.

Correct Answer: A — 1/2

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Q. What is the probability of selecting a vowel from the English alphabet?

A. 1/5
B. 1/10
C. 1/26
D. 1/13

Solution

There are 5 vowels (A, E, I, O, U) in the English alphabet of 26 letters. Therefore, P(vowel) = 5/26.

Correct Answer: A — 1/5

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Probability Basics

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