It would be an odd number. Starting from think of pairs of numbers adding up to 11. 1 and 10....hmm that won't do. 2 and 9, yes. 3 and 8, no. 4 and 7, yes. 5 and 6, no. 6 and 5, yes. 7 and 4, no. 8 and 3 yes. 9 and 2, no. 10 and 1, no (three digits altogether). Ans, 29, 47, 65, 83.
