(i) Find the number of integers between 500 and 5000 that do not contain 0 as a digit.

(ii) How many integers between 500 and 5000 contain the digit 0 exactly once?

(iii) ...at least twice?

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Assuming that 500 and 5000 are not included,

(i)

(ii)

(iii)

I assume these are right(ish), but is there a simpler method?