1) To estimate quickly, round numbers to values that allow for mental math, do the calculation with simplified numbers, and check if the estimate seems reasonable. 2) Percentage error compares the difference between an estimate and actual value relative to the actual value, with a smaller percentage error indicating a more accurate estimate. 3) Standard form (scientific notation) expresses very small or large numbers as a coefficient between 1 and 10 multiplied by a power of 10, such as 1.23x103 for 1,230 or 3.47x10-2 for 0.0347.