Our number system is based on multiples of 10.  That makes multiplying or dividing by 10, 100, or 1000 very easy!  We count the number of zeroes and shift by that many places.

• To multiply by 10, we shift the place value of each digit to be one place larger.
  To multiply by 100, we shift the place value of each digit to be two places larger.
  To multiply by 1000, we shift the place value of each digit three places larger.
  Ex: 34.09 x 1000 = 34,090

• Dividing by 10, 100, or 1000 works the same way, but we shift to make the place value smaller by the number of 0's.
  Ex: 25.6 ÷ 100 = 0.256

To convert between metric units, begin in the column for the unit you are given.  Then jump to the column of the new units.  Use the arrows at the bottom to determine how to multiply or divide.

Example:  5.2 meters = ___ millimeters

• Begin in unit (meter)

• Jump three columns right --> means x1000

• 5.2 x 1000 = 5,200 millimeters

Adding, subtracting, multiplying, and dividing with decimals is almost the same as with whole numbers!  We just need to keep track of where the decimal goes (a.k.a., pay attention to place value).

Skip to the following time stamps in the video if you want to review a specific operation:

• Addition - 0:57

• Subtraction - 3:15

• Multiplication - 3:40

• Division - 7:55 (note, we will not divide by a decimal divisor in 5th grade)

We use rounding and compatible numbers to help us estimate decimal multiplication and division.  Remember, the point of rounding is to find numbers that are easier to think about so you can find an approximate answer (one that is reasonably close to the exact answer).