How many counting numbers less than 100000 have only even digits?
99 000 or less
5 choices for each digit
55 = 3125
You're really close, but the first digit only has 4 options since it can't be 0.
4*5*5*5*5 = 2500
I've made a dumb error... >:(((
So I forgot that numbers exist that aren't 5 digit.-.-
So please ignore that previous response.
As for why the 2 guests have gotten different answers is because 0 is also counted using the method: 5^5 = 3125, so you just have to subtract 1.
Nice job to our guests for solving the problem... I'm quite sad that I've made such a dumb mistake.