Page 20 - Start Up Mathematics_6

Estimation or rounding off the 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 19: Using the above mentioned procedure, estimate the following numbers to their
nearest tens.
(a) 74 (b) 167 (c) 3,421 (d) 46,785

Solution: (a) In the number 74, the digit at ones place is 4. Since 4 < 5, we replace it by 0.
Therefore, estimate of 74 is 70.
(b) In the number 167, the digit at ones place is 7. Since 7 > 5, we replace it by 0
and add 1 to the digit at tens place, i.e., add 1 to 6. Therefore, estimate of 167
is 170.
(c) In the number 3,421, the digit at ones place is 1. Since 1 < 5, we replace it by
0. Therefore, estimate of 3,421 is 3,420.
(d) 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, estimate of 46,785 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.

Example 20: Using the above mentioned procedure, estimate the following numbers to their
nearest hundreds.
(a) 374 (b) 143 (c) 3,421 (d) 46,785

Solution: (a) In the number 374, the digit at tens place is 7. Since 7 > 4, we replace digits at
tens and ones place by 0 and add 1 to hundreds place. Therefore, estimate of
374 to its nearest hundreds is 400.
(b) 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, estimate of 143 to its nearest hundreds is
100.
(c) In the number 3,421, the digit at tens place is 2. Since 2 < 5, we replace digits
at tens and ones place by 0. Therefore, estimate of 3,421 to its nearest hundreds
is 3,400.

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