2) It is called Base Ten because I think you multiply by ten when you move past the decimal sign. (Well, sort of. You do multiply by ten when you move to the left of the decimal sign, going from the ones place, to the tens place, to the hundreds place, etc.)
3) I think it is called Base Ten because it's something we use everyday. (Really????)
Enough! It is called Base Ten because we use ten digits (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9) to write all of the other numbers. Each digit can have one of ten values: any number from 0 through 9. When the value reaches 9, just before 10, it starts over at zero again. (Notice the pattern below.)
In addition, each place is worth ten times more than the last. Ten is worth ten times more than 1, and 1,000 is ten times more than 100. The pattern continues infinitely both ways on a number line.
The decimal point allows for the place value to continue in a consistent pattern with numbers smaller than one. As we move to the right of the decimal point, each place is divided by ten to get to the next place value. One hundredth is one tenth divided by ten, and one thousandth is one hundredth divided by ten. The pattern goes on infinitely.
100's, 10's, 1's . 0.1, 0.01, 0.001, 0.0001, 0.00001, etc.
Since all mathematics is based on patterns, this should not be a new revelation. Perhaps on the post-test, my students will omit the fingers and instead rely on patterns to answer the questions!