the coupon problem.
Look at the Calculating the expectation section for the answer.
So I've been having some massive trouble with this problem and after bashing my head and doing all else possible, I came here.
Question: There are 6 toys included in a happy meal. Each is equally likely to be in the happy meal. Find the # of happy meals that you would need to buy to get all 6 toys ON AVERAGE.
Ignore the bold at your peril.