133%
You commute by bus each day to work and it takes thirty-three minutes going to work and thirty-three minutes coming home at the end of the day. You would say that it takes you about one hour on the bus.
These are examples of estimating.
You have already learned about rounding numbers. You need to be able to round numbers in order to be able to estimate.
When you solve math problems, it is a good idea to estimate what the answer may be. Estimating the answer means finding an answer that is close to the real answer. Estimating helps you to see if the real answer is sensible. To estimate an answer, you need to round the numbers then add or subtract the rounded numbers. Remember to round to the nearest ten.
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Example: |
23 + 45 |
Estimate: |
20 + 50 |
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|
|
70 |
|
Example: |
67 |
Estimate: |
70 |
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|
─ 31 |
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─ 30 |
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|
40 |
|
Example: |
372 |
Estimate: |
370 |
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|
+ 416 |
|
+ 420 |
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|
|
790 |
|
Example: |
564 |
Estimate: |
560 |
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|
─ 243 |
|
─ 240 |
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|
|
|
320 |
Exercise OneEstimate the following answers. Be sure to round to the
nearest 10 before adding. Check your work using the answer key at the end of the exercise.
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a)27 |
Estimate: |
b)42 |
Estimate: |
|
+ 31 |
|
+ 51 |
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|
c)26 |
Estimate: |
d)14 |
Estimate: |
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+ 32 |
|
+ 52 |
|
|
e)44 |
Estimate: |
f)31 |
Estimate: |
|
+ 24 |
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+ 27 |
|
|
g)65 |
Estimate: |
h)46 |
Estimate: |
|
+ 22 |
|
+ 23 |
|
|
i)23 |
Estimate: |
j)42 |
Estimate: |
|
+ 72 |
|
+ 36 |
|
|
k)64 |
Estimate: |
l)32 |
Estimate: |
|
+ 14 |
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+ 20 |
|
|
m) 423 |
Estimate: |
n) 526 |
Estimate: |
|
+ 324 |
|
+ 345 |
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|
o) 123 |
Estimate: |
p) 752 |
Estimate: |
|
+ 541 |
|
+ 243 |
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|
q) 429 |
Estimate: |
r) 324 |
Estimate: |
|
+ 316 |
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+ 115 |
|
|
s) 162 |
Estimate: |
t)156 |
Estimate: |
|
+ 531 |
|
+ 322 |
|
|
u) 302 |
Estimate: |
v) 326 |
Estimate: |
|
+ 473 |
|
+ 607 |
|
|
w) 312 |
Estimate: |
x) 341 |
Estimate: |
|
+ 148 |
|
+ 248 |
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Answers to Exercise One |
|||||||||||||
|
a) |
60 |
b) |
90 |
c) |
60 |
d) |
60 |
e) |
60 |
f) |
60 |
g) |
90 |
|
h) |
70 |
i) |
90 |
j) |
80 |
k) |
70 |
l) |
50 |
m) |
740 |
n) |
880 |
|
o) |
660 |
p) |
990 |
q) |
750 |
r) |
440 |
s) |
690 |
t) |
480 |
u) |
770 |
|
v) |
940 |
w) |
460 |
x) |
590 |
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|
|
|
|
|
|
Exercise TwoEstimate the following answers. Be sure to round to the
nearest 10 before subtracting. Check your work using the answer key at the end of the exercise.
|
a)35 |
Estimate: |
b)52 |
Estimate: |
|
─ 16 |
|
─ 14 |
|
|
c)67 |
Estimate: |
d)51 |
Estimate: |
|
─ 19 |
|
─ 23 |
|
|
e)36 |
Estimate: |
f)72 |
Estimate: |
|
─ 17 |
|
─ 44 |
|
|
g)38 |
Estimate: |
h)74 |
Estimate: |
|
─ 19 |
|
─ 26 |
|
|
i)93 |
Estimate: |
j)82 |
Estimate: |
|
─ 89 |
|
─ 57 |
|
|
k)56 |
Estimate: |
l)94 |
Estimate: |
|
─ 27 |
|
─ 48 |
|
|
m) 752 |
Estimate: |
n) 765 |
Estimate: |
|
─ 342 |
|
─ 439 |
|
|
o) 673 |
Estimate: |
p) 645 |
Estimate: |
|
─ 424 |
|
─ 309 |
|
|
q) 811 |
Estimate: |
r) 591 |
Estimate: |
|
─ 502 |
|
─ 57 |
|
|
s) 972 |
Estimate: |
t)178 |
Estimate: |
|
─ 447 |
|
─ 15