Rounding

Decimal Places - count from the decimal point

Significant Figures

1. Count from the first digit.
2. Don't count zeros unless they're in-between non-zero digits.

Estimating

1. Use one significant figure unless you can be more accurate and still do it in your head.

Error

1. Measurement is only approximate.
2. The real answer can be half the rounded unit either way.
3. We call them upper and lower bounds.

Maximum values of calculations:

1. Addition and Multiplication - use all upper bounds.
2. Subtraction and Division - first number upper bound, second number lower bound.

Vice versa for minimum values of calculations.

Trial and Improvement

1. Use tables to display guesses and answers. Say whether too high or too low!
2. Be methodical.
3. If you know which two numbers the answer is between try the middle and that will tell you which one it is closer to.