# Probability question

I can't seem to get the correct answer for this probability question:

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

(a) if the first ball is replaced

(b) if the first ball is not replaced

I could do these.

Then there is a bit at the end which says:

If 2 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 its associated probability.

I can do the bit on a) as getting a total score of 8 has the greatest probability according to my diagram, which is 1/7, but I don't know how to do it for part b). The answer is 7,8,9 -> 1/7, but I can't see how they got this.

Thanks
sweet_gurl
I can't seem to get the correct answer for this probability question:

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

(a) if the first ball is replaced

(b) if the first ball is not replaced

I could do these.

Then there is a bit at the end which says:

If 2 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 its associated probability.

I can do the bit on a) as getting a total score of 8 has the greatest probability according to my diagram, which is 1/7, but I don't know how to do it for part b). The answer is 7,8,9 -> 1/7, but I can't see how they got this.

Thanks

Here is first part... didn't read all the way through.. so didn't seer you could do this one... Is my answer the same as yours.
Yes it is the same. I just don't understand the last part of the question.
I havent looked at the guys iamge but remember that once the ball is out theres only 6 left. its simple but often overlooke.d
If you draw a tree diagram, you will find the probability of getting a 7,8 or 9 would be 1/7 * 1/6 * 6 = 6/42 = 1/7 for each number.