SOLUTION: A box contains six discs numbered 1 to 6. Find for each integer k from 3 to 11, the probability that the number on two discs have a sum equal to k.

Question 1163823: A box contains six discs numbered 1 to 6. Find for each integer k from 3 to
11, the probability that the number on two discs have a sum equal to k.

Answer by Edwin McCravy(20059) (Show Source): You can put this solution on YOUR website!

You didn't state that correctly, because what you asked for,

"the probability that the number on two discs have a sum equal to k"

the answer is 1 for every value of k, because it's ABSOLUTELY CERTAIN that
there are two discs in the box whose numbers on them have sum equal to 
each integer k=3,4,5,6,7,8,9,10,11.

So the probability in every case is 1.  Surely that's not what you are 
asked to find.

What you didn't state was that 

YOU ARE GOING TO DRAW TWO DISCS OUT OF THE BOX!!!

If you don't draw any discs out of the box, the probability is 1 that some
pair of them in the box have each of those sums.

So resubmit the problem, stating that you are going to draw two of the discs
out of the box, not just leave all 6 of them in the box.  Get it?

Edwin

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