1. Knowing Our Numbers Worksheet With Answers Page 14
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25·
Mark a point O on it.
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Label the point O as ‘0’.
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Now mark points on the right hand side of ‘0’ at equal distances as 1, 2, 3, 4, 5, ... and so on.
O
0
1
2
3
4
5
...
The line shown above is a number line representing whole numbers. We observe that the number
on the left hand side is smaller than the number on the right hand side. For example, since 2 is on
the left of 5 on the number line therefore 2 < 5.
Rounding Off the Numbers Using Number Line
Let’s learn the concept of rounding off the numbers with the help of number line.
(i) Estimate 43 to its nearest tens.
Step 1: Let’s draw a number line including numbers from 40 to 50.
0
10
20
30
40 43
50
Step 2: Now, observe whether 43 is nearer to 40 or 50.
Step 3: Clearly, 43 is nearer to 40. Therefore, estimated value of 43 to its nearest tens
is 40.
(ii) Estimate 478 to its nearest hundreds.
Step 1: Let’s draw a number line including numbers from 400 to 500.
0
400
100
200
300
478 500
600
Step 2: Now, observe whether 478 is nearer to 400 or 500.
Step 3: Clearly, 478 is nearer to 500. Therefore, estimated value of 478 to its nearest
hundreds is 500.
(iii) Estimate 2,500 to its nearest thousands.
Step 1: Let’s draw a number line including numbers from 2,000 to 3,000.
0
2,500
3,000
1,000
2,000
4,000
6,000
5,000
Step 2: Now, observe whether 2,500 is nearer to 2,000 or 3,000.
Step 3: Clearly, 2,500 is neither nearer to 2,000 nor to 3,000. Actually, it is in the middle
of both. In such a situation, as a rule we do not take the smaller estimated number.
Therefore, estimated value of 2,500 to its nearest thousands is 3,000.
Estimation in Sum or Difference
There is no rigid rule to estimate a number. We can round off a number to any place (tens, hundreds
or thousands) depending upon the degree of accuracy required. The most important aspect of
estimation or rounding off is that the estimated value should make sense.
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