1. Knowing Our Numbers Worksheet With Answers Page 12
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25‘Five thousand people gathered for a political meeting.’
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‘A mob of six hundred armed people attacked the police station in Chhattisgarh.’
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In fact, no one counted the exact number of people present for the particular event. It is only a
general idea about the gathering in each case.
Nine hundred could be 876 or 908 or thirty thousand could be 29,034 or 30,136.
If exactly 30,219 workers attended a political meeting, we say that about 30,000 people were
present for the said meeting. If 193 teachers from Delhi attended a workshop then, it may be said
that about 200 teachers from Delhi attended the workshop. The exact number could be a little
less or more than the number which we have stated. This process of getting a general idea of the
number is called estimation. Estimation of numbers is done to the nearest tens, hundreds,
thousands, ..., i.e., 10, 100, 1,000, ... .
The estimation of numbers is also known as rounding off numbers.
Estimation or Rounding Off Numbers to the Nearest Tens
Procedure:
Step 1: In the given number, examine the digit at ones place.
Step 2: If the digit at ones place is less than 5, i.e., 0, 1, 2, 3, or 4, replace it by 0 and rest of the
digits remain unchanged.
Step 3: If the digit at ones place is 5 or greater than 5, i.e., 5, 6, 7, 8 or 9, replace it by 0 and add
1 to the digit at tens place.
Example 21: Using the above mentioned procedure, estimate the following numbers to their
nearest tens.
(a) 74
(b) 163
(c) 3,421
(d) 46,785
Solution:
(a) In the number 74, the digit at ones place is 4. As per the procedure, we need to
replace 4 at ones place by 0. Therefore, estimate of the given number is 70.
(b) In the number 163, the digit at ones place is 3. As per the procedure, we need to
replace 3 at ones place by 0. Therefore, estimate of the given number is 160.
(c) In the number 3,421, the digit at ones place is 1. As per the procedure, we need
to replace 1 at ones place by 0. Therefore, estimate of the given number is 3,420.
(d) In the number 46,785, the digit at ones place is 5. As per the procedure, we need
to replace 5 at ones place by 0 and add 1 to the digit at tens place, i.e., add 1 to
8. Therefore, estimate of the given number is 46,790.
Estimation or Rounding Off the Numbers to the Nearest Hundreds
Procedure:
Step 1: In the given number, examine the digit at tens place.
Step 2: If the digit at tens place is less than 5, i.e., 0, 1, 2, 3, or 4, replace the digits at tens and ones
place by 0 each and rest of the digits remain unchanged.
Step 3: If the digit at tens place is 5 or greater than 5, i.e., 5, 6, 7, 8 or 9, replace the digits at tens
and ones place by 0 and add 1 to the digit at hundreds place. The rest of the digits remain
unchanged.
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