Estimating and scales

• Significant figures = digits in a number that tell us how precise a number is
• zeros between digits are always significant.
• zeros before first digit is not significant
• Round 3.14159 to 3 significant figures

  1. Identify the first 3 digits: 3.14
  2. Look at the next digit (1)
  3. Round down if next digit is 4 or lower
• When adding or subtracting number with different decimal places, round the answer to the least number of decimal places.
• 47 + 23 = 50 + 20 = 70
• Estimate the $\sqrt{19}$


  $4^2$ = 16 but $5^2$ = 25.

  The square root of 19 must be between 4 and 5
• Dividing a number by 0.5 is the same as multiplying by 2