Posted by PLEASE HELP on Monday, February 20, 2012 at 4:18am.
With one digit, there are three possibilities, 5, 7 and 8
With two digits, there are 3^2 = 9 possibilites:
55, 57, 58
75, 77, 78,
85, 87, 88.
With three digits, there are 3^3 = 27 possibilities.
3 + 9 + 27 = 39
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