So you limited yourself to non-negative integers, and had no idea what negative numbers or fractions would do.

Also he didn't know what numbers whose digits add up to 88 would do.

Their input on the phone wouldn't allow minus or period characters so I assumed positive integers were the set.

Based on the context of the question and the UI of the testing interface, fractions seem unlikely to be an intended part of the question. I likewise wouldn't bother testing unicode U+216x roman numerals.

It refused to accept both fractions and imaginary numbers. I did test negatives and zeros since that was really the only remaining set I could think of.

Most importantly I used about 6 tests (3 right 3 wrong) to come up with the answer and then did another 17 looking for the trick. After all, it couldn't just be that simple right?

The presentation of the problem -- and I know that trusting the problem state is unwise sometimes in cognitive-bias tests, since many such tests are actually designed to be "we said we were asking X but actually meant Y" -- indicated a simple rule, rather than one which would behave differently on different classes of numbers.

So after the tests listed above I felt confident enough to guess.

[16 32 64] [0 0 0] [1 2 3] [3 2 1] [-1 0 1] [3 5 7] [-2 -1 0] [111 54231 9999999999999999999999]

At that point, I correctly answered the question.

Similar to mine, but we both actually failed. Real numbers are accepted and we did not test that.

It accepts floating point numbers. To approximately double precision.

But it accepts zero percent of real numbers.

I can nitpick better than that!

To talk about a certain fraction of real numbers you have to have a distribution over them. In general we take the uniform distribution if no distribution is explicitly given. That doesn't work for real numbers (it doesn't even work for natural numbers). (See https://math.stackexchange.com/questions/14777/why-isnt-ther...)

If there's no implicit default distribution, we have to pick on. I can pick one where they cover an arbitrary high percentage of real numbers..

Down the rabbit hole of pedantry: we don't need a distribution, just a measure, if we want to talk about how many reals it accepts. The Lebesgue measure is implied on the Reals if none is given, and the computable reals have measure zero.

We can't reasonably talk about a percent coverage, since the Lebesgue measure of the reals is infinite, but as a non-technical description, 'zero percent' is morally equivalent to saying it only covers a measure-zero set.

I did this plus also testing [1 1.5 2]