Answers & Explanation:
1) Answer: D
Total number of balls = 10 + x
Required probability
= > 6/(10 + x) = 2/5
= > 10 + x = 15
= > x = 5
Total number of balls in the basket = 10 + 5 = 15 balls
2) Answer: B
Total event=(HHH, HHT, HTH, THH, THT, HTT, TTH, TTT)
=8
Possible ways =(THT, HTT, TTH)=3
Required probability=3/8
3) Answer: A
Total event=(1, 2, 3, 4, 5, 6)
Possibility of getting Prime number=(2, 3, 5)
Required probability=3/6=1/2
4) Answer: D
The number of kings in the pack=4
Total number of cards=52
Required probability=4C2 /52C2 = (4 * 3)/(52 * 51)
=1/221
5) Answer: B
Required probability=4C2/7C2
= (4 * 3)/(7 * 6)
=2/7
6) Answer: A
Required probability=5C2 / 9C2