Math...Probabilty

2009-01-05 12:25 am

1. In a family of three children, what is the probabilty that at least two of the children are girls?
2. What is the total number of possible outcomes in throwing four coins?
3. In rolling two dice, what is the probabilty of getting a double?
4.A bag contains 3 red,2 green and 1 blue balls. If two balls are drawn without replacement, find the chance of getting all green.
5.A bag has six $20 notes and eight $50 notes. If a note is selected at random, what is the probabilty of getting a $50 note?
6.Sam puts four red balls, three blue balls and five white balls into a box. He chooses a balll randomly from the box.Find the probabilty that a) he gets a blue ball, b) he does not get a blue ball.
7. There are five boys and two girls in a van. If one of them is chosen at random to get off the van, find the probabilty that two girls remain in the van.
8. A bag contains five apples, eight pears and ten oranges. If Mary chooses a fruit at ranom, find the probabilty that she does not gat an apple.

回答 (1)

老爺子

2009-01-05 2:18 am

✔ 最佳答案

1.
G = girl, B = boy
P(at least two girls)
= P(two girls) + P(3 girls)
= P(BGG) + P(GBG) + P(GGB) + P(GGG)
= 4(1/2)3
= 1/2

2.
Each coin has two sides: head and tail
Total number of possible outcomes
= (2)4
= 16

3.
Each die has 6 faces.
Total number of possible outcomes of throwing two dice
= (6)2
= 36

Number of possible outcomes of getting a double (double 1, 2, 3, 4, 5, 6)
= 6

P(getting a double)
= 6/36
= 1/6

4.
P(getting all green)
= P(1st is green from 6 balls, 2nd is green from 5 balls left)
= P(1st is green from 6 balls) * P(2nd is green from 5 balls left)
= (2/6) * (1/5)
= 1/15

5.
Total number of notes = 6 + 8 = 14
Number of $50 notes = 8

P(getting a $50 notes)
= 8/14
= 4/7

6.
Total number of balls = 4 + 3 + 5 = 12
Number of blue balls = 3

a)
P(getting a blue ball)
= 3/12
= 1/4

b)
P(not getting a blue ball)
= 1 - 1/4
= 3/4

7.
Total number of children = 5 + 2 = 7

P(two girls remain in the van)
= P(a boys is chosen to get off the van)
= 5/7

8.
Total number of fruit = 5 + 8 + 10 = 23

P(not getting an apple)
= 1 - P(getting an apple)
= 1 - 5/23
= 18/23
=

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