A bakery produces six different kinds of pastry, one of which is eclairs. Assume there are at least 20 pastries of each kind.

a) How many different selections of twenty pastries are there?
I was thinking combinations with repetition and order doesn't matter, so (n+r-1 r) but I'm not sure where n=120 and r=20?

b) How many different selections of twenty pastries are there if at least three must be eclairs?
(n+r-1 r) = (120+20-1 20) = (139 20) (20 3) ???

c) How many different selections of twenty pastries contain at most two eclairs?

(139 20) (20 2) ??

Question

A bakery produces six different kinds of pastry, one of which is eclairs. Assume there are at least 20 pastries of each kind. 

a) How many different selections of twenty pastries are there? 
I was thinking combinations with repetition and order doesn't matter, so (n+r-1 r) but I'm not sure where n=120 and r=20? 

b) How many different selections of twenty pastries are there if at least three must be eclairs? 
(n+r-1 r) = (120+20-1 20) = (139 20) (20 3) ??? 

c) How many different selections of twenty pastries contain at most two eclairs? 

(139 20) (20 2) ??

anonymous · Answer

I need helping solving this problem. Please explain it to me in a logical fashion and a step by step mental process on how to think about it and how to approach it and why the formulas work. I know you have to compound the formula on parts b and c but I'm a little confused on how to do it. 

Thanks a lot!
9 minutes ago -