Fraction Rules: For addition and subtraction, find a common denominator (lowest common multiple) first. For multiplication, multiply numerators and denominators straight across. For division, multiply by the reciprocal of the second fraction (keep, change, flip). Always reduce the final fraction to its simplest form using the greatest common divisor.
Decimal Rules: For addition and subtraction, align the decimal points vertically. For multiplication, ignore the decimals, multiply as integers, and then place the decimal point so the result has the sum of the decimal places of the factors. For division, multiply both the divisor and dividend by powers of 10 to make the divisor a whole number, then divide.