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Ben twice chooses a random integer between 1 and 50, inclusive (and he may choose the same integer both times). What is the probability that at least one of the numbers Ben chooses is a multiple of 3?

 Jan 9, 2017

Best Answer 

 #5
avatar+33616 
+6

When you get a question with "at least" in, it is often a good idea to find the probability of "none" first, then the probability of "at least" = 1 - probability of "none".

 

Suppose there are n integers between 1 and 50 that are not multiples of 3.  Then the probability of choosing a random integer that is not a multiple of 3 is n/50.

 

The probability of doinjg this twice is (n/50)^2.  Hence the probability that at least one number is a multiple of 3 is 1 - (n/50)^2

 Jan 9, 2017
 #1
avatar+221 
-5

What difficulties are you having with this problem? Don't expect people to solve your math problems for you. That is called cheating.

 Jan 9, 2017
 #4
avatar+556 
+4

Okay. I don't get what you are suposed to fill in for these cases. 

Case 1:

First pick multiple of 3

Second pick not multiple of 3.

 

Case 2:

First pick not multiple of 3

Second pick multiple of 3

 

Case 3:

Both picks multiples of 3

 

Isn't this like a math forum so.....

arnolde1234  Jan 9, 2017
 #2
avatar
-3

Why are ALL your questions about "Probability"? Is that all you know, or don't know?

 Jan 9, 2017
 #3
avatar+556 
+4

I am currently taking a course in Counting and Probability andi am posting the questions I don't understand onto here. I have also posted some Geometry questions too so.....

arnolde1234  Jan 9, 2017
 #5
avatar+33616 
+6
Best Answer

When you get a question with "at least" in, it is often a good idea to find the probability of "none" first, then the probability of "at least" = 1 - probability of "none".

 

Suppose there are n integers between 1 and 50 that are not multiples of 3.  Then the probability of choosing a random integer that is not a multiple of 3 is n/50.

 

The probability of doinjg this twice is (n/50)^2.  Hence the probability that at least one number is a multiple of 3 is 1 - (n/50)^2

Alan Jan 9, 2017

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