SOLUTION: A pair of dice are rolled 20 times. What is the probability that: A sum of seven is rolled at least 3 times? What is the expected number of sums of seven for 20 rolls?

There are 6 way to get a 7
1+6,2+5,3+4,4+3,5+2,6+1

There are 36 ways the dice can come up.
P(7) = 1/6

On your TI-83 or 84 with the menu at 2ND VARS

1 - binomcdf(20,1/6,2)

0.6713409285

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Expected number = np = 20(1/6) = 20/6 = 

[It will never be  times, but if you rolled
20 times ecery day for a year, and averaged up the number 
of 5's each day for the whole year it would be about .

Edwin