mathschallenge.net

Problem

In the equation,

2 *

* 5

=

1 15

The * symbol stands for the same whole number value. Find its value.

Solution

By trial,

2 3

3 5

=

10 15

9 15

=

1 15

Is there a more efficient way to solve this problem?

What about

* 9

7 *

=

1 72

?