Multiplying and dividing
Multiply and divide whole numbers and those involving decimals by 10, 100, and 1000
What a learner can do afterwards
- Calculate 3.45 × 100 = 345
- Calculate 72 ÷ 1000 = 0.072
- Explain that multiplying by 10 shifts each digit one place to the left
The lesson
You already know that multiplying by 10 moves each digit one place to the left in the place-value chart. Multiplying by 100 moves every digit two places to the left, and multiplying by 1000 moves every digit three places to the left. This same rule works for decimal numbers, not just whole numbers.
To multiply 3.45 by 100, move every digit two places to the left in the place-value chart. The 3 moves into the hundreds place, the 4 moves into the tens place, and the 5 moves into the ones place. The digits line up as 345.
To divide 72 by 1000, move every digit three places to the right instead. The 7 moves into the hundredths place and the 2 moves into the thousandths place. The empty places get filled with zero, so 72 divided by 1000 equals 0.072.
Count the zeros in 10, 100, or 1000. That tells you how many places to shift. Multiplying shifts digits left and makes the number bigger. Dividing shifts digits right and makes the number smaller.
Multiplying shifts digits left and dividing shifts digits right, by as many places as the zeros in 10, 100, or 1000.
Watch it
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.