//------------------------------//
// The Answer 31 
// Story: Life is A Test 2: Test Harder (Quite A Bit Harder) 
// by Brony_of_Brody 
//------------------------------//

Record the mass of every single pack. The smallest difference in mass between any two readings must be equal to the smallest difference in amount of Prism Poppers - in other words, the mass of a single sweet.

However, this only works if the number of sweet packets is large enough for you to be sure that you'll have packs with consecutive whole number totals.