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There is
good news and bad news about this lesson.
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The good news: there is a
shortcut for multiplying and dividing decimals! |
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The bad news: it only
works when multiplying if one of the factors is a power
of 10. It only works for dividing if the divisor is
a power of 10. |
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OK, but you ask,
"What's a power of ten?" |
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So 10, 100,
1,000, 10,000 etc. are powers of ten, and that's what
you can use for this shortcut! |
Let's start with some examples:
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5.9 x 10 = 59 |
3.99 x 10 = 39.9 |
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58.54 x 100 = 5854 |
79.6 x 100 = 7960 |
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0.988 x 10 = 9.88 |
3.56 x 1000 = 3560 |
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9.88 x 1000 = 9880 |
0.837 x 10 = 8.37 |
Look carefully.
Sooooooo......:
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to multiply by 10,
move the decimal point one place to the right
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to multiply by 100,
move the decimal point two places to the right
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to multiply by
1,000, move the decimal point three places to the right
Now, what about
division?
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5.1 ÷ 10 =
0.51 |
23.78 ÷ 10 =
2.378 |
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19.88 ÷ 10 =
1.988 |
490 ÷ 100 =
4.9 |
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47 ÷ 100= 0.47 |
3.788 ÷ 1000 =
0.003788 |
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0.765 ÷ 100 =
0.00765 |
25,678 ÷ 1000
= 25.678 |
Do you see a
pattern here?
Sooooooo......:
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to divide by 10,
move the decimal point one place to the left
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to divide by 100,
move the decimal point two places to the left
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to divide by 1,000,
move the decimal point three places to the left
Ready
for some practice?
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