1. Significant Figures The amount of significant figures in a number tells us how accurate the number is. When we look at a number we should treat all figures as significant unless they are zeros at the start of a decimal. Ex1 7856.0047 sig figs Ex2 56.04 4 sig figs Ex3 0.000708 3 sig figs

2. Timed Exercise - How many Sig Figs In? 1) 78.932) 5.0089 5 3) 506.0 44) 210 3 5) 0.0897 3 6) 0.00000056 2 7) 0.009008 48) 0.0009 1

3. FOR DISCUSSION - DON’T COPY !!!! The number 4587 has 4 sig figs ie Th, H, T & U If we round this to two sig figs thenwe lose the T & U. So 4587 becomes4600

4. FOR DISCUSSION - DON’T COPY !!!! The number 3458.7 has 5 sig figs ie Th, H, T, U & t If we round this to three sig figs thenwe lose the U & t. So 3458.7 becomes3460

5. Example 1Round 230.6 to two sig figs This has 4 sig figs 230.6 = 230 Example 2Round 308761 to three sig figs This has 6 sig figs 308761 = 309000 Example 3 Round 0.0008731 to two sig figs This has 4 sig figs 0.0008731 = 0.00087

6. Round each of the following to two significant figures.. TIMED EXERCISE 2 1) 3.456 2) 67302 3) 567902 4) 12.389 5) 0.09765 6) 0.98013 7) 0.0000876 8) 0.0090007 3.5 67000 570000 12 0.098 0.98 0.000088 0.0090

7. One Sig Fig Approximations By rounding numbers to one sig fig we can find approximate answers to calculations Ex1 378.96 X 67.9 X 0.4668 = 400 X 70 X 0.5 = 14000 Ex2 195.6  53.1 = 200  50 = 4

8. Ex3 Which of the following could be the answer to 19.8 X 5.23  11.3 ? (a) 9276(b) 916.7(c) 93.64(d) 9.164 19.8 X 5.23  11.3 becomes 20 X 5  10 = 10 So answer (d).