Bunuel
A team contributes a total of $399 from its members. If each member contributed at least $10, and no one contributed $19, what is the greatest number of members the club could have?
A. \(37\)
B. \(38\)
C. \(39\)
D. \(40\)
E. \(41\)
No cases are required here. Think of it in this way:
Everyone must contribute at least $10. Since I need the greatest number of members, each should contribute the least possible. The least possible is $10. But that gives us 39.9 members which is not possible.
This means that some people contributed a bit more to get the total to 399. Everybody did not give exactly $10. Since I want to maximise the number of members, I say perhaps some contributed $11 then and all others gave $10 only. So from 399, I remove some multiples of 11 to be left with a multiple of 10. If I remove one 11, I get 388 which is not a multiple of 10. If I remove 2 11s, I get 377 which is not a multiple of 10. So I have to keep removing.
When I remove 9 11s from 399 I will get 300.
So 9 people could have contributed $11 and 30 people could have contributed $10. Then total will be $399. So 39 people is possible.
Of course 40 is not possible as the answer because then we would have at least $400 collected.
Answer (C)