fistful is possibly from the slide rule days when order of magnitude (decimal point placement) had to be estimated / figured separately. There was no way to enter 0.9 into a slide rule, or, for that matter, 0.45.
Thus, 45 ÷ 9 = 5
450 ÷ 900 = 5
4.5 ÷ .009 = 5
45,000 ÷ 9 = 5
And 5 = 50
Terry runs and hides