1. LETS REVIEW SIGNIFICANT FIGURES ONE MORE TIME Solving Problems with Significant Figures

2. Multiplying and Dividing Significant Figures Suppose you measure a room and find that it is 22 feet long and 9 feet wide. 22 (length) has two significant figures and 9 (width) has one significant figure. The area of the room is length X width Area= 22 feet X 9 feet =198 square feet which rounded to 200 square feet.

3. Why was the answer rounded to one significant figure? When multiplying or dividing measurements, the answer must have the same number of significant figures as the measurement with the fewest significant figures. If the answer has more significant figures, it has to be rounded to the correct number of significant figures

4. Sometimes, a number in a problem is not a measurement, it might be a defined number. A defined number is part of a definition and is not measured

5. For example, suppose you want to measure something that is 725 centimeters long. You want to change it to meters. You know that there are 100 CMs in a M. You would divide 725/100 and get 7.25 Meters Since 100 has only one significant answer does this mean the answer should be rounded to 7? No. The number 100 is part of a definition. Defined numbers do not limit the significant figures in an answer

6. In another case, a number in a problem might be a counting number. Say you have a 28 inch submarine and you want to divide it evenly into 5 pieces to serve 5 people. Counting numbers, like defined numbers do not limit significant figures. 28/5 = 5.6 inches of sandwich per person

7. Adding and Subtracting with Significant Figures When adding and subtracting the answer must have the same number of significant figures to the right of the decimal point as the measurement with the fewest significant figures to the right of the decimal point. When needed, round the correct number of significant figures. Digits to the left of the decimal are not counted in the rule

8. Example 4.271 grams 2 grams +10.0 grams 16.271 grams which is rounded to 16 grams WHY is it ROUNDED?

9. One measurement, 2 grams, has 0 significant figures to the right of the decimal point. Therefore, the answer must have 0 significant figures to the right of the decimal point.