2009 UNCO Math Contest II Problems/Problem 1
Problem
How many positive -digit numbers are there such that For example, and have this property but and do not.
Solution
Here, we need to find such that , and where .
If we place , then we can place as , i.e. in ways.
Similarly, if we place , we can place i.e. in ways.
If, we place , we have the only choice , in ways.
So, in order to get the number of possibilities, we have to add the no. of all the possibilities we got, i.e. the answer is
See also
2009 UNCO Math Contest II (Problems • Answer Key • Resources) | ||
Preceded by First Question |
Followed by Problem 2 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 | ||
All UNCO Math Contest Problems and Solutions |