# Probability Quiz Set 002

### Question 1

A class has 7 boys and 2 girls. What is the probability of choosing 1 boy and 2 girls?

A

\${1/12}\$.

B

\$8/9\$.

C

\$2/12\$.

D

\$6/12\$.

Soln.
Ans: a

Three students have to be picked. Total number of ways = 9C3 = \${9 × 8 × 7}/{3 × 2 × 1} = \$84. Number of ways of picking 1 boy and 2 girls = 7C1 × 2C2 = 7. So probability = \$7/84\$ = \${1/12}\$.

### Question 2

A dice is thrown once. What is the probability that we get a number greater than 4?

A

1/3.

B

2/3.

C

5/6.

D

1.

Soln.
Ans: a

Total outcomes = 6. Favorable outcomes are 2: getting a 5 or 6. The required probability is 2/6 = 1/3.

### Question 3

What is the probability of getting a head when a coin is tossed in the air?

A

1.

B

1/2.

C

1/4.

D

0.

Soln.
Ans: b

Total outcomes are 2, H or T. The number of favorable chances for heads is 1. So probability is 1/2.

### Question 4

A box contains 82 red balls and an unknown number of blue balls. If the probability of drawing a blue ball is 2 times the probability of drawing a red ball, then how many blue balls are there in the box?

A

164.

B

169.

C

159.

D

174.

Soln.
Ans: a

Let the number of blue balls be x. Chances of drawing a blue ball are \$x/{x + 82}\$ = 2 × \$82/{x + 82}\$, which gives x = 2 × 82 = 164.

### Question 5

A class has 5 boys and 3 girls. What is the probability of choosing 1 boy and 2 girls?

A

\${15/56}\$.

B

\$6/8\$.

C

\$16/56\$.

D

\$20/56\$.

Soln.
Ans: a

Three students have to be picked. Total number of ways = 8C3 = \${8 × 7 × 6}/{3 × 2 × 1} = \$56. Number of ways of picking 1 boy and 2 girls = 5C1 × 3C2 = 15. So probability = \$15/56\$ = \${15/56}\$. 