Problem:
When three positive integers a,b, and c are multiplied together, their product is 100. Suppose a<b<c. In how many ways can the numbers be chosen?
Answer Choices:
A. 0
B. 1
C. 2
D. 3
E. 4
Solution:
The factors of 100 are 1, 2, 4, 5, 10, 20, 25, 50, and 100. Consider each possible value of a and determine whether there are any solutions given that aβ
bβ
c = 100 and a<b<c.
If a=1, then bβ
c = 100. There are 3 solutions: 1β
2β
50, 1β
4β
25, and 1β
5β
20.
If a=2, then bβ
c=50. There is 1 solution: 2β
5β
10.
If aβ₯4, then bβ
cβ€25. There are no solutions given that a<b<c.
In summary, there are 4 ways to choose the numbers a, b, and c:
100=1β
2β
50=1β
4β
25=1β
5β
20=2β
5β
10.
Answer: Aβ.
The problems on this page are the property of the MAA's American Mathematics Competitions