Page 25 - ICSE Math 6

Example 14: Estimate the following numbers to the nearest tens.
(a) 74 (b) 46,785

Solution: (a) In the number 74, the digit at ones place is 4. Since 4 < 5, we replace it by 0.
Therefore, the estimation of 74 to the nearest tens is 70.
(b) In the number 46,785, the digit at ones place is 5. So, we replace it by 0 and add
1 to the digit at tens place, i.e., add 1 to 8. Therefore, the estimation of 46,785 to
the nearest tens is 46,790.

Estimation or rounding off the numbers to the nearest hundreds
The steps to estimate or round off a given number to the nearest hundreds are as follows:
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 both the digits at tens
and ones place by 0 and leave the remaining digits unchanged.
• 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.
Example 15: Estimate the following numbers to the nearest hundreds.

(a) 143 (b) 46,785
Solution: (a) In the number 143, the digit at tens place is 4. Since 4 < 5, we replace digits at tens
and ones place by 0. Therefore, the estimation of 143 to the nearest hundreds is 100.
(b) In the number 46,785, the digit at tens place is 8. Since 8 > 5, we replace both the
digits at tens and ones place by 0 and add 1 to the digit at hundreds place. Therefore,
the estimation of 46,785 to the nearest hundreds is 46,800.

Estimation or rounding off the numbers to the nearest thousands
The steps to estimate or round off a given number to the nearest thousands are as follows:
Step 1: In the given number, examine the digit at hundreds place.
Step 2: • If the digit at hundreds place is less than 5, i.e., 0, 1, 2, 3, or 4, replace the digits at
hundreds, tens and ones place by 0 and leave of the remaining digits unchanged.
• If the digit at hundreds place is 5 or greater than 5, i.e., 5, 6, 7, 8 or 9, replace the digits
at hundreds, tens and ones place by 0 and add 1 to the digit at thousands place.

Example 16: Estimate the following numbers to the nearest thousands.

(a) 1,374 (b) 3,621
Solution: (a) In the number 1,374, the digit at hundreds place is 3. Since 3 < 5, we replace digits
at hundreds, tens and ones place by 0. Therefore, the estimation of 1,374 to the
nearest thousands is 1,000.
(b) In the number 3,621, the digit at hundreds place is 6. Since 6 > 5, we replace digits
at hundreds, tens and ones place by 0 and add 1 to the digit at thousands place.
Therefore, the estimation of 3,621 to the nearest thousands is 4,000.

Estimation in sum or difference
The most important aspect of estimation or rounding off is that the estimated value should make sense.
There is no rigid rule to estimate a number. We can round off a number to any place depending upon
the degree of accuracy required.

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