An m&m is like an atom: smallest unit of an element, in this case the smallest unit for a m&ms in general (larger unit= a bag, a big bag, etc.). like a mole for atoms, the ammount in a 'bag' is a number of UNITS. what matters for a mole is that there are 6.022*10^23 atoms. what matters for m&ms is the amount (count of m&ms as UNITS) that you have. atoms of the same element may be differant isotpes, and so weigh more or less than other atoms of the same isotope, and peanut m&ms can weigh slightly differant ammounts but they are still peanut m&ms. are you going to say that, because the peanut m&ms vary silghtly in weight, they should be measured by wieght instead of unit? so that, if you buy a "family size" bag of m&ms, the serving size will say something like, 'serving size: 22.36 m&ms'? think of the problems that would pose to weight watchers: i bet you can't eat just .36! that would be like saying that a more precise way to get a mole is to count out exactly 6.022*10^23 atoms. the exactness is not so important anyway, that ammount of the precision itself would be an inaccurate representation of the question, because whats the point of saying, oh, you can buy 40.492 m&ms for a dollar, when you can only either get 40 m&ms or 41 m&ms. They come in WHOLE NUMBER AMMOUNTS (remember DALTON'S laws? we have a chem final coming up!), so why bring in decimals????? anyway, you can collect data on the bag over a period of time. and you get to eat more m&ms.

To prove my point once again, i found this conclusive study on the internet: