Can 0 be a denominator? Or can a # be divided by 0?
No, it's undefined.
How should you add/subtract decimals?
Line the decimals up, then add/subtract. Add zeroes behind #s if necessary.
How should you multiply decimals?
Multiply them as if whole #s, then insert decimal later. Add decimal point so that the sum of the #s to the right of the decimal equals the sum of #s to the right of the decimals in your original #s.
Ex:
2.09 (2 right of decimal)
x 1.3 (1 right of decimal)
= 2.717 (3 right of decimal)
When dividing a # by a decimal...
Change the dividend (# on left) to a whole #. Then move the decimal in the divisor (# on right, under line), the # of spaces you had to move the decimal in the dividend to make a whole #.