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When Trilisa takes pictures, they turn out with probability 1/5. She wants to take enoughpictures so that the probability of at least one turning out is at least 3/4. How few pictures can she take toaccomplish this?

 Jan 19, 2021
 #1
avatar+536 
+1

If it 1 has to make it, then we can find the probability of none making it and work from there. If the probability wanted is 3/4, then 1/4 is the chance they all don't make it. So (4/5)^x has to be less than .25.

 

The smallest number is 7

 Jan 20, 2021
 #2
avatar+116126 
+1

Each picture she takes has a probability  of (4/5)  of  not  turning out

 

The probability  of  at  least one turning  out  = 1 - probability that  none turn out

 

 

So we have

 

1  - (4/5)^n    = 3/4               where n is the number of pictures she needs to take

 

1 - 3/4   = (4/5)^n

 

1/4 = ( 4/5)^n            take the  log of  both sides

 

log (1/4) / =  log (4/5)^n

 

log (.25)  = log(.8)^n     and we can write

 

log (.25)  = n * log(.8)

 

n=  log (.25)/log (.8)    ≈  6.21

 

So..as 4M found  ......she needs to take  7

 

 

cool cool cool

 Jan 20, 2021

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