What is the least number of students that could be enrolled in a school so that you can be sure that there are at least two students with the same birthday? 

Eight marbles all have the same size, color, and shape. Seven of them have the same weight and the other is heavier. Using a balance scale, how would you flnd the heavy marble if you make only two weighings?

Is it possible to measure out exactly 2 gallons using only an 8 gallon container and a 5 gallon container? The containers do not have individual gallon markings or any other markings.