Significant Digits
Any Nonzero Number [1, 2, 3, 4, 5, 6, 7, 8, 9]  is Significant

Determining Which Zeros are Significant
1.
 Zeros holding the decimal point are not significant. Zeros that end a whole # or start a decimal # are not significant.  The zeros in the examples to the right are not significant.
 2,000
35,000
50
.0008
.02
.0000745
2.
 Zeros between nonzero digits are significant.  Examples to the right show zeros that are significant.
 309
1,500,725
.205
3.
 Zeros at the end of a number that are to the right of the decimal point are significant. Zeros that you would normally drop but don't.  Examples to the right.
 45.0
.87500
.350
225.70
Determine the number of significant digits in each of the following:
1)  34,800,000
 2)  40
 3)  .000075
 4)  205
 5)  .002045
 6)  .0000620
Answers:
1)  3
 2)  1
 3)  2
 4)  3
 5)  4
 6)  3

Rounding your answer to the correct number of significant digits
Addition and Subtraction: Round the answer to the smallest place value known in every number.
Examples:
21.8
  4.912
+2.75  
29.462  Answer: 29.5
68.92
- 2.1  
66.82  Answer:  66.8
17.586
- 2.63  
14.956 Answer:  14.96
 502
  25.95
+  4.8  
532.75  Answer:  533

Multiplication and Division:   Round the answer to the least number of digits.
Examples:
52 x 5 =260
Answer:  300
 260/.07 = 3714.2857
Answer:  4000
 7540 x .0020 = 15.08
Answer:  15
 45.9/7.382 = 6.217827
Answer:  6.22

Solve:
1)  18.6 + 25 + 2.785 =
 2)  34.76 - 21.8 =
 3)  5.786 + 2.43 + 8.542 =
4)  4.0 x 6.3 =
5)  67.0/45.7 =
 6) 3450 x 20.50 =
Answers:
1)  46
 2)  13.0
 3)  16.76
 4)  25
 5)  1.47
 6)  70,700