A bag holds 7 red, 8 blue and 4 green balls. You draw one at random. What is the probability P that it is blue?
Probability worksheet with answers
1.Easy
7 / 8 / 4
P =
2.Easy
Two fair dice are rolled. What is the probability P that the sum is exactly 8?
2 dice= 8
P =
3.Medium
A bag holds 5 red and 6 blue balls. You draw two balls without putting the first one back. What is the probability P that both are red?
5 / 6
P =
4.Medium
In how many ways N can a committee of 3 people be chosen from a group of 15? The order does not matter.
n = 15k = 3
N =
5.Hard
A game costs €3 to play. You win €12 with probability 0.25 and €150 with probability 0.02; otherwise you win nothing. The stake is not returned. Find the expected net gain E(G) per game.
stake = €3€12: p = 0.25€150: p = 0.02
E(G) = €
6.Hard
X has the distribution shown, and Y = 0.5X + 10. Find the standard deviation σY of Y.
x: 1, 2, 3, 4, 5p(x): 0.3, 0.2, 0.2, 0.25, 0.05Y = 0.5X + 10
σY =
Answer key
- 1. P = 0.4211
- 2. P = 0.1389
- 3. P = 0.1818
- 4. N = 455
- 5. E(G) = 3 €
- 6. σY = 0.6418
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