2.  There are 2 kinds of numbers:  Exact: the amount of money in your account. Known with certainty.  Approximate: weight, height— anything MEASURED. No measurement is perfect.

3.  If you measured the width of a paper with your ruler you might record 21.7cm.  To a mathematician 21.70, or 21.700 is the same.

4.  21.700cm to a scientist means the measurement is accurate to within one thousandth of a cm.

5.  If you used an ordinary ruler, the smallest marking is the mm, so your measurement has to be recorded as 21.7cm.

6.  Rule: All digits are significant starting with the first non-zero digit on the left.

7.  Exception to rule: In whole numbers that end in zero, the zeros at the end are not significant.

8.  7  40  0.5  0.00003  7 x 10 5  7,000,000 11 11 11 11 11 11

9.  2nd Exception to rule: If zeros are sandwiched between non-zero digits, the zeros become significant.

10.  3rd Exception to rule: If zeros are at the end of a number that has a decimal, the zeros are significant.

11.  3rd Exception to rule: These zeros are showing how accurate the measurement or calculation are.

12.  1.2  2100  56.76  4.00  0.0792  7,083,000,000 22 22 44 33 33 44

13.  3401  2100  2100.0  5.00  0.00412  8,000,050,000 44 22 55 33 33 66

14.  Rule: When adding or subtracting measured numbers, the answer can have no more places after the decimal than the LEAST of the measured numbers.

15.  2.45cm + 1.2cm = 3.65cm,  Round off to = 3.7cm  7.432cm + 2cm = 9.432 round to  9cm

16.  Rule: When multiplying or dividing, the result can have no more significant digits than the least reliable measurement.

17.  56.78 cm x 2.45cm = 139.111 cm 2  Round to  139cm 2  75.8cm x 9.6cm = ?

18. 1) 5.40 ____ 6) 1.2 x 103 ____ 2) 210 ____ 7) 0.00120 ____ 3) 801.5 ____ 8) 0.0102 ____ 4) 1,000 ____ 9) 9.010 x 10- 6 ____ 5) 101.0100 ____ 10) 2,370.0 ____