



 
Hi Mel, One way to look at this is arrangements of 12 O's (donuts) and 4 's (dividers between the boxes of donuts) so that, for example OOOOOOOOOOOO means that you buy 3 donuts of the first type, none of the second type, 5 of the third type, 3 of the fourth type, and 1 of the fifth type. So what you need to figure out is how many ways can you arrange 12 O's and 4 's in a line. The best way to think of this is in how many ways can you place the 12 O's into the 16 places which is ... . Penny
 


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