Grade 4 - Progress in Mathematics

Estimate with Decimals

13-7

Rounding is one way to estimate

decimal sums and differences.

To estimate sums or differences with decimals:


Round the decimals to the greatest nonzero

place of the lesser number.


Then add or subtract.

Estimate: 123.6 
8.43 Estimate: 78.61 0.45

 123 .6 
 124 
78. 61 
78.6


 8 .43 
 8  0. 45  0.5

about
 132 about
78.1

Study these examples.


0. 92 
0.9 
4. 7 
4.7 
 8 .8 
 9


0. 37 
0.4 0. 18 0.2 
 5 .1 
 5

about
1.3 about
4.5 about
 14

Round to estimate the sum or the difference. Watch the signs.

1. 
   5.9 2.
   9.7 3.
   8.75 4.
   9.38 5.
   4.91
   
   3.2 4.6 1.17
   6.04
   6.73


2. 
   42.3 7.
   38.5 8.
   56.2 9.
   27.8 10.
   85.43
    6.7
   5.8  4.84
   6.65  1.7


3. 
   0.85 12.
   10.3 13.
   62.77 14.
   48.5 15.
   26.21
   
   0.63  0.81
   9.84  0.69
   0.59


4. 
   74.36 17.
   62 18.
   49.95 19.
   405.5 20.
   380.4
   
   18  7.8  5.2  5.76
   2.35


5. 4.5
   39.03 22. 17.03 1.5 23. 47 6.62

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