Abank teller has some stacks of bills. the total value of the bills in each stack
is $1000. every stack contains at least one $20 bill, at least one $50 bill, and no
other types of bills. if no two stacks have the same number of $20 bills, what is the
maximum possible number of stacks that the teller could have?
(a) 9 (b) 10 (c) 11 (d) 4 (e) 8

So since only 20 dollar bills and the other one is a 50
then

so we find some combos that will work
five 20's make 100
we notice that we can only have 20's in multipules of 5 to make 100's becauause 4 20's makes 80 and 3 20's make 60 and 2 20's make40 and none of those add to 50 evenly to make 100's
(probably confusing but I hope you understand if you think about it)

so we have
5 20's =100
10 20's=200
15 20's=300
20
25
30
35
40
45 20's=900
50 20's=1000

so how many multiplules did we have?
10
but wait, if we havve 1000 in all 20's we still need at least one 50 so we subtract 100
900:9
answe ris 9 stacks

answer is 9 stacks or A