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Adding decimals with hundredths
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Tagging a zero On the number line you see that 0.2 = 0.20 and 0.3 = 0.30. How can that be?
On the other hand, if you tag a zero to the number 47, you get 470. Are these equal? Why? |
1. Fill in the chart. Tag a zero in the end, and compare the numbers.
| Before | After | Before | After | ||||||||||||||||||||||||||||||||||||||||||||
| a. |
4.5 |
= |
4.50 |
c. |
408 |
4080 |
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| d. |
0.6 |
0.60 |
f. |
105.4 |
105.40 |
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The numbers are equal if ______________________________________________________.
2. Write the decimals as fractions. Add the fractions. Add the
decimals. Compare.
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1.12 + 0.23 + 0.03 =
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What about when one addend has hundredths, and the other only tenths?? Try add the following:
| 0.2 + 0.05 = | 0.7 + 0.04 = | 0.12 + 0.5 = |
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[number line available in the ebook]
0.2 + 0.05 = ____ If you are at 0.2 and go five hundredths (0.05) further, where will you end up?
Let's check the other two problems you did earlier. Write the problems also using fractions.
0.7 + 0.04 = ____ If you are at 0.7 and go four hundredths further, where do you end up? 0.12 + 0.5 = ____ If you are at 0.5 and go twelve hundredths further, where do you end up? |
Practice.
3. Add mentally. Pay close attention to the number that only has tenths. Before adding, tag a zero to it so the addends will have the same amount of decimals. Write the problems using fractions also.
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0.6 + 0.09 = | |||||||||||||||
| 0.11 + 0.5 = | 0.3 + 0.39 = |
4. Continue the patterns.
| 0.06 + ___ = 0.09
0.06 + ___ = 0.10 0.06 + ___ = 0.11 0.06 + ___ = ____ 0.06 + ___ = ____ 0.06 + ___ = ____ 0.06 + ___ = ____ |
0.5 + ___ = 0.55
0.5 + ___ = 0.57 0.5 + ___ = 0.59 0.5 + ___ = ____ 0.5 + ___ = ____ 0.5 + ___ = ____ 0.5 + ___ = ____ |
5. Add. Then explain the fundamental difference between the two problems. Discuss with your teacher.
| 0.03 + 0.02 = | 0.03 + 0.9 = |
6. Complete the addition sentences. Compare the top and bottom ones.
Remember how 0.4 = 0.40 !
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7. Explain why the following additions are wrong: a) 0.99
+ 0.1 = 1 b)
0.43 + 0.59 = 0.102
8. How many hundredths do you need to add to make the next whole tenth?
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Adding or subtracting decimals with hundredths in columns works the usual way, just line up the decimal points and add a decimal point to the answer! If the decimals are not the same length, tag a zero to the end of the shorter one. Make sure the decimal points line up! |
| Estimate your answer first so you can catch gross errors in calculations. When estimating, round the numbers so that you can easily add or subtract them mentally. See the examples below |
9. Add or subtract in columns. Estimate first!
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a. Estimation: 70 + 2 = 72 |
d. Estimation: |
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| e. 52.42 − 1.88 |
h. 17.95 + 9.99 | |
| Estimation: | Estimation: |
| m. 5776.6 − 2901.48 |
p. 2049.05 − 56.06 | |
| Estimation: | Estimation: |
10. Word problems.
| a) The world record for 400m race is 43.18 seconds for men (Michael
Johnson), and 47.60 seconds for women (Marita Koch). How much is the
time difference?
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| c) Mike buys bread for $1.56, butter for $2.34, and a can of beans
for $0.78. How much is his total bill? How much change will he
get from $5?
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Next lesson: Add decimals with hundredths, part 2
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The ideas in this decimals lesson are taken from Math Mammoth Decimals 1 book ($4.00 download). Only a few examples of each problem type are shown. |
The fast, FUN, and easy way to learn multiplication. Learn the upper times tales in two sittings using mnemonic stories.
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Copyright 2003-2013 Maria Miller
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