# What's up with my calculator?

As I am wont to do, I got a new calculator the other day. Obviously it needed a few test calculations:

5 + 6 = 11
22 - 17 = 5
10 + 3 = 13
4 * 6 = 24


OK, so far so good. But there were also a bunch of weird results that I don't understand:

2 * 1 = 10
9 + 7 = 9
3 - 1 = 3
34 - 8 = 2


What's going on?

replacing the numbers with how many segments they have lit up on a standard 7-segment display, and doing the calculations with those. (For example, "22" has 10 segments and "17" has 5 segments, so "22 - 17" turns into 10 - 5, which is 5.)

• He's good! You can't fool Deus! May 31 '19 at 1:11
• Exactly right, well done! May 31 '19 at 7:12