For example, we say that the distance between the earth and the sun is about 93,000,000 miles when actually it is 92,897,416 miles.
In our daily lives we often use estimation or approximation whenever we are asked the question "How many?" or "How much?" or other quantitative questions. For instance, how big is the damage caused by a volcanic eruption, then we may say billions of dollars worth of properties and other infrastructures has been damaged.
Examples above show the need to round off numbers. Rounding off numbers to the nearest tens, thousands, etc. depends on the quantity. For example, a number of students in a class may only be rounded off to the nearest tens, but a rally can be attended by hundreds or thousands or even millions of people.
How to round off numbers to an indicated place:
1: If the digit to be dropped from a number is less than one-half of the indicated place value, then just drop the digit and replace it with zeroes.
2: If the digit to be dropped from a number is one-half or more of the place value indicated, add 1 to the digit in that place and replace the digit dropped with zero.
Examples. Round off to the indicated place.
1. 652 to the nearest tens
Solution:
The numeral in the tens place value is 5.
The numeral we need to drop in the number is 2.
But 2 is lesser than 10÷2=5, so we only replace 2 with 0 such that we have 650.
2. 879 to the nearest hundreds
Solution:
The numeral in the hundreds place is 8.
The numerals we need to drop are 7 and 9.
Now, 79 is greater than 100÷2=50, so we add 1 to 8 and replace the digits dropped with zero such that we have 900.
3. 145,000 to the nearest ten thousands
Solution:
Since 5,000 is half of the indicated place value, 10,000÷2 then the answer is 150,000.
Try the following: Round off each number to the indicated place:
| tens | hundreds | thousands | |
|---|---|---|---|
| 8,631 | 8,630 | 8,600 | |
| 1,577 | 1,580 | 2,000 | |
| 2,395 | 2,400 |
| hundred thousand | million | |
|---|---|---|
| 2,671,003 | 2,600,000 | |
| 739,629,126 | 740,000,000 | |
| 21,669,400 | 21,700,000 |
