1. in a school, 46% of the students are full time, 49% are female, and 22% are male full time.find the prob that a student chosen at random from all female students is part time.
2. in a group of 356 people, 109 own a cat, 121 own a dog, 43 own a cat and a dog.
(a)what is the prob a person chosen owns a cat given that he owns a dog.
(b)that is the prob a person dose not own a cat given that he owns a dog.
3.a number is drawn from integers from 177 to 2121
(a) what is the prob that it is a multiple of 3 given that it is a even.
(b) what is the prob that it is a multiple of 5 given that it is a multiple of 3.
Probability
2014-12-14 9:37 pm
回答 (1)
2014-12-16 12:57 am
✔ 最佳答案
1.male full time = 22%
female full time = 46% - 22% = 24%
female part time = 49% - 24% = 25%
P(part time | female)
= P(part time & female) / P(female)
= 25% / 49%
= 25 / 49
2.
P(owns a cat | owns a dog)
= P(own a cat & a dog) / P(own a dog)
= (43 / 356) / (121 / 356)
= 43 / 121
P(does not own a cat | own a dog)
= 1 - P(owns a cat | owns a dog)
= 1 - (43 / 121)
= 78 / 121
3.
from 177 to 2121, there are 1945 nos.
from 177 to 2121, there are (2121 - 177) / 3 + 1 = 649 nos. are multiples of 3.
from 178 to 2120, there are (2120 - 178) / 2 + 1 = 972 nos. are even.
from 180 to 2118, there are (2118 - 180) / 6 + 1 = 324 nos. are multiples of 6.
from 180 to 2120, there are (2120 - 180) / 5 + 1 = 389 nos. are multiples of 5.
from 180 to 2115, there are (2115 - 180) / 15 + 1 = 130 nos. are multiples of 15.
P(multiple of 3 | even)
= P(multiple of 3 & even) / P(even)
= P(multiple of 6) / P(even)
= (324 / 1945) / (972 / 1945)
= 1 / 3
P(multiple of 5 | multiple of 3)
= P(multiple of 5 & multiple of 3) / P(multiple of 3)
= P(multiple of 15) / P(multiple of 3)
= (130 / 1945) / (649 / 1945)
= 130 / 649
參考: knowledge
收錄日期: 2021-04-28 14:21:54
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