A fair 2

A fair die is thrown two times. What is the probability that the sum of the score is almost 8?

Correct answer:

p =  0.8333

Step-by-step explanation:

1+1 1+2 1+3 1+4 1+5 1+6  2+2 2+3 2+4 2+5 2+6  3+3 3+4 3+5  4+4  n=6+5+3+1=15  p=6 62 n=6 62 15=0.8333



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Showing 2 comments:
Math student
By "almost 8", did you mean "at most 8"?

It's appropriate, in your solution, to double the number of ways to get a total of at most 8 on different outcomes, but it's not appropriate to double the number of times you roll doubles (so 1+1, 2+2, 3+3, 4+4).  Therefore, your 30/36 figure over-counts by 4.  The correct answer is 26/36.  Another way to reach this is to look at a 6-by-6 grid of ordered pairs: (1,1) through (6,6).  Diagonals have a constant sum: 1 way to roll 2, 2 ways to roll 3, ..., 6 ways to roll 7, 5 ways to roll 8.  Answer: (1+2+3+4+5+6+5)/36=26/36.

10 months ago  3 Likes
Hmp
I agree with Math student above.

9 months ago  1 Like




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