Question

What is the two-digit number N?

Statements

1. The tens digit of N is 4.
2. The sum of the digits of N is 9.

Answer

Both statements together are sufficient, but neither alone is sufficient.

Solution

1. Statement 1 allows 40 through 49.
2. Statement 2 allows many two-digit numbers whose digits add to 9.
3. Together the units digit is 5, so N = 45.