Digits & Decimals

Things one must know:

• Place value: hundreds digit x 100 + tens digit x 10 + units digits x 1
• Use variables for unknown digits, xy and the reverse yx
• If the right-digit-neighbor is 5 or greater, round up
• Multiplying by powers of ten moves decimal forward specified number of places, dividing moves the decimal back. Negative powers reverse the regular process
• To find the units digit of a product or a sum of integers, only pay attention to the units digits of the numbers.
• Heavy Division Shortcut: move the decimals in the same direction and round to whole numbers
• Powers and roots: rewrite the decimal as the product of an integer and a power of ten, and then apply the exponent