Rounding is a way to change a number to a shorter or simpler number that is very close to the original number. There are a lot of different ways to round numbers. We will discuss the most common way here.
When to Round Up or Down
When rounding a number you will "round up" or "round down". When the number you are rounding is between 0-4, you round down to the next lowest number. When the number is 5-9, you round the number up to the next highest number.
Round the numbers below to the nearest 10:
87 ----> round up to 90
45 ----> round up to 50
32 ----> round down to 30
Rounding to a Place Value
When we round a number, we round it to the nearest place value. This could be the tens, hundreds, thousands, etc. It could also be to the right of the decimal point where we would round to the nearest tenths, hundredths, etc.
Round the following numbers to the hundreds:
459 ----> 500
398 ----> 400
201 ----> 200
145 ----> 100
Round the following numbers to the tenths:
99.054 ----> 99.1
7.4599 ----> 7.5
52.940 ----> 52.9
80.245 ----> 80.2
Rounding a "9"
What do you do when you have to round up a "9"? Let's say you have to round the number 498 to the nearest tens place. Because there is an 8 in the ones place, you need to round up the nine, but there isn't any single digit higher than 9! In this case you make the "9" a "0" and round up the "4" to a "5". Therefore, 498 rounded to the nearest tens place is 500.
1) Round 3.895 to the nearest hundredths place:
There 9 is in the hundredths place. The next number to the right is 5, so we want to round the 9 up. We must make the 9 a 0 and then round the 8 up.
Note: We keep the "0" even though it is to the right of the decimal place. This shows that the number has been rounded to the hundredths place.
2) 4.9999 to the thousandths place
3) 19,649 to the nearest thousand
Rounding for a Word Problem
Before you can round a number, you need to know what place value you are rounding to. Sometimes a problem may state specifically what place value (like the tenths or the hundreds) that you need to round to. Other times the problem may state that you need to round to a specific measurement like to the nearest cent in money. Always make sure you understand what you need to round to before you round.
Round the following to the nearest cent:
$ 47.3456 ----> $ 47.35
$ 12.4744 ----> $ 12.47
$ 99.998 ----> $ 100.00
Things to Remember
- If the number is 0-4 ----> round down
- If the number is 5-9 ----> round up
- You need to know what place value you are rounding to.
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