How many two-digit numbers have non-zero digits whose sum is prime?
I don't know a way to do this except by brute force.
What "brute force" means, in mathematics, is that you just try everything.
Like so:
12, 14, 16
21, 23, 25, 29
32, 34, 38
41, 43, 47, 49
52, 56, 58
61, 65, 67
74, 76
83, 85, 89
92, 94, 98
I stacked them like that to see if I could detect a pattern. I couldn't.
I made this list quickly in my head so I might've missed one/some.
If I didn't overlook one/some, the total is 28. Check my work.
.
