This is a sequence of two-digit numbers, and the last number is missing. Can you identify the final number and tell what these two-digit numbers (but no others) have in common? Good luck!
10, 11, 12, 13, 15, 20, 30, 40, ?
Here is the ANSWER.
And why? These are the only two-digit numbers whose names don't incorporate the spelling of a single digit - zero, one, two, three, four, five, six, seven, eight, or nine.
Of all two-digit numbers, only ten, eleven, twelve, thirteen, fifteen, twenty, thirty, forty and fifty do NOT incorporate the spelling of a single-digit number.
All other two-digit numbers (ex: sixteen, twenty-nine, fifty-eight, sixty, eighty-one, ninety-four) contain the spelling of at least one single digit.
Thanks for playing!