remove the subscript (i); you want the full array here.
NB: Do NOT redefine the builtin function mean() by using mean as a variable name.
Reading the code a little more thoroughly, I think
isn't what you want, though.
If I read the problem description correctly, it is the distribution for each part that is given; you're only generating 10 random parts but then multiplying that by the number of parts of each type per box. The box weights would be
Then your simulation needs to create 15 of these boxes for each pallet if you want to keep statistics on the distribution of box weights in addition to the overall pallet weight.
Or, if you only care about pallets, then you could increase the number of samples by 15X and then the total weight would be the estimate for the pallet for each realization.
It would be far better coding practice to have all the "magic" constants defined as variables at the beginning of the script/function. Then, one could change any parameter at will without having to rewrite the code to handle it.