Formula and example
How it is calculated
With m missing designs out of N: expected draws=N·Σ(1/i), i=1…m. New designs after t draws: m·[1−(1−1/N)^t].
Worked example
If only one of 100 equally common designs is missing, finding it takes an average of 100 further draws. The next sticker has a 1% chance of being that design.
Things to check
- The model assumes independent draws and equal frequencies. Guaranteed packet contents, rare designs and swaps change the result.
- Expected duplicates also include repeat copies of a design first found during the planned purchase.
Frequently asked questions
Does an average of 100 draws mean the sticker will arrive by then?
No. An average is not an upper limit. A particular collection can be completed sooner or take considerably longer.