Proability (1 Viewer)

[fire and ice]

Hey guys,

can anyone do these question for me

A tank contain 20 tagged fish and 80 untagged fish. On each day, four fish are selected at random, and after nothing whether they are tagged or untagged, they are returned to the tank. Answer the following to 3 sig fig. What is the proaability of selecting no tagged fish on exactly three of the seven days during the week? Ans 0.291

A bag contain seven white and five black discs. Three discs are choosen from the bag. Find the probability that all three discs are black, if the discs are choosen: so that after each draw the disc is replaced with one of the opposite colour. Ans 5/144

The digits 1,2,3,4 are used to form numbers that may have 1,2,3,4 digits in them. If one of the numbers it selected at random, find the probability that:
i) it is greater than 200 ans 21/32
ii) it is divisble by 3 ans 17/64

Any help is appreciated.

 

[braintic]

Hey guys,

can anyone do these question for me

A tank contain 20 tagged fish and 80 untagged fish. On each day, four fish are selected at random, and after nothing whether they are tagged or untagged, they are returned to the tank. Answer the following to 3 sig fig. What is the proaability of selecting no tagged fish on exactly three of the seven days during the week? Ans 0.291

A bag contain seven white and five black discs. Three discs are choosen from the bag. Find the probability that all three discs are black, if the discs are choosen: so that after each draw the disc is replaced with one of the opposite colour. Ans 5/144

The digits 1,2,3,4 are used to form numbers that may have 1,2,3,4 digits in them. If one of the numbers it selected at random, find the probability that:
i) it is greater than 200 ans 21/32
ii) it is divisble by 3 ans 17/64

Any help is appreciated.

1. Probability of no tagged fish on a particular day = 60/80 times 59/79 times 58/78 times 57/77 = a mess
Probability of exactly 3 days with no tagged fish = 7C3 times (a mess)^3 times (1 - a mess)^4

 

[HeroicPandas]

Hey guys,

can anyone do these question for me


The digits 1,2,3,4 are used to form numbers that may have 1,2,3,4 digits in them. If one of the numbers it selected at random, find the probability that:
i) it is greater than 200 ans 21/32
ii) it is divisble by 3 ans 17/64

Any help is appreciated.

(i)Find total first:

1 number: 4
2 number:4 x 3
3 numbers: 4 x 3 x 2
4 numbers: 4 x 3 x 2 x 1

These are mutually-exclusive events and so we add them = 64

For numbers >200, we must obtain 3 or more digits

3 numbers: 3 x 3 x 2 (first number must be 2, 3, 4. after u pick 1, three numbers are left to pick, then 2 numbers are left to pick)
4 numbers: 4x3x2x1 (thousands are greatre than hundreds)

Same thing, add them = 42

P(number >200) = 42/64 = 21/64

(ii) i cant think of a quick way... (add all digits,if divislbe by 3, then the number is divisble by 3)

 

[Girls]

A bag contain seven white and five black discs. Three discs are choosen from the bag. Find the probability that all three discs are black, if the discs are choosen: so that after each draw the disc is replaced with one of the opposite colour. Ans 5/144

You have 12 disks at first and 5 of them are black, thus the probability is 5/12 that you will pull out a black disk.
After drawing that black disk though, a white one is put in its place so you still have 12 disks in the bag but one less black one i.e. P=4/12.
That process is then repeated a third time so the probability of the third disk being black is 3/12.

We then multiply the probabilities together to get the probability that all three are black:
5/12 x 4/12 x 3/12

=5/144

Hope that helps.