Question 723992: Please help with an explanation!!!
Roll a pair of dice. Find the probability of getting either a sum of 7 or atleast one 5.
For the sum of 7, I got 1/6.
For the atleast one 5, I got 11/36.
Here is where I get lost, The probability of (sum of 7 AND atleast one 5) = 1/18.
Explain where the 1/18 comes from so I can understand the remaining problems, and how to solve them. Thank you dearly
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! Roll a pair of dice.
Find the probability of getting either a sum of 7 or atleast one 5.
For the sum of 7, I got 6/36.
For the at least one 5, I got 11/36.
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The probability of (sum of 7 AND atleast one 5) = 1/18.
Explain where the 1/18 comes from so I can understand the remaining problems, and how to solve them.
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P(sum of 7 AND at least one 5) = P(sum of 7) + P(at least one 5)
- P(sum of 7 OR at least one 5)
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= (6/36) + (11/36) - (15/36) = (2/36) = 1/18
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Note: The 15/36 comes from 6 where 5 is 1st ; 6 where 5 is 2nd ;
6 where the sum is 7 ; and 3 that satisfy 2 conditions and have
been counted twice: 6+6+6-3 = 15
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Cheers,
Stan H.
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