The problems of counting with fingers

While waiting for Mommy buying some groceries, I took the girls to a nearby 7-11 and let them pick their choice of sweets. Also, because of Kristine's problems with money, I decided to teach her and also test her at the same time:

Me: OK, your sweets costs RM1.00 and Kaelynn's is RM0.60. How much is that?
Kristine: Erm..... One dollar... sixty sen.....
Me: Think of the one dollar as 10 and the sixty as six...
Kristine: .... its sixteen!
Me: Yes, and now, its actually, RM1.60. Now, if I give you RM2.00 for you to give to Koh-Koh there, how much will he give back?
Kristine: ... erm... sixten.... um... twenty..... (after a very long time...) But Dad, I don't have 20 fingers!
Me: ...