If our target number is 28 then we can create all of the following factor pairs for this number. These would be the following...
1, 2, 4, 7, 14 and 28
As we can see from the factor pairs there is no 3. This means that 3 would not divide evenly by 28 and cannot be multiplied by any whole number to create 28. Therefore, if you divide the 28 stickers by the 3 friends there will be some stickers leftover always.
