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# Statistics 1 Probability Help! Watch

1. (I put down my working for the first two parts of the question in case it's necessary for attaining the solution to part c) )

Seven identical balls are marked respectively with the numbers 1 to 7 inclusive. The number on each ball respresents the score for that ball. The seven balls are then put into a bag. If 2 balls are chosen at random on after the other, find the probability of obtaining a total score of 11 or more:

a) if the first ball is replaced
b) if the first ball is not replaced
c) if two balls are chosen at random one after the other from the 7 balls, find, in case a) and in case b), the most probable total score for the 2 balls with it's associated probability.

For a)

I listed all the combinations that total 11: 77,76,75,74,66,65,67,57,47,56

= 10/49 (7 balls x 7 balls = 49 outcomes in total)

For b)

I simply cancelled out the outcomes where the same ball comes out twice (77,66,55,44,33,22,11)

i.e 7 less outcomes 'possible' outcomes and 2 less outcomes that total to 11

=4/21

c) if two balls are chosen at random one after the other from the 7 balls, find, in case a) and in case b), the most probable total score for the 2 balls with it's associated probability. (??)

Help appreciated.

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Updated: December 15, 2010
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