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Rounding Numbers

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.

Example:

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.

Examples:

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.

Example problems:

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.

Answer: 3.90

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

5.000

3) 19,649 to the nearest thousand

20,000

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.

Example:

Round the following to the nearest cent:

$ 47.3456 ----> $ 47.35
$ 12.4744 ----> $ 12.47
$ 99.998 ----> $ 100.00

Things to Remember



Kids Math Subjects

Multiplication
Intro to Multiplication
Long Multiplication
Multiplication Tips and Tricks
Square and Square Root

Division
Intro to Division
Long Division
Division Tips and Tricks

Fractions
Intro to Fractions
Equivalent Fractions
Simplifying and Reducing Fractions
Adding and Subtracting Fractions
Multiplying and Dividing Fractions

Decimals
Decimals Place Value
Adding and Subtracting Decimals
Multiplying and Dividing Decimals

Misc
Basic Laws of Math
Inequalities
Rounding Numbers
Significant Digits and Figures
Prime Numbers
Roman Numerals
Binary Numbers 		Statistics
Mean, Median, Mode, and Range
Picture Graphs

Algebra
Exponents
Linear Equations - Introduction
Linear Equations - Slope Forms
Order of Operations
Ratios
Ratios, Fractions, and Percentages
Solving Algebra Equations with Addition and Subtraction
Solving Algebra Equations with Multiplication and Division

Geometry
Circle
Polygons
Quadrilaterals
Triangles
Pythagorean Theorem
Perimeter
Slope
Surface Area
Volume of a Box or Cube
Volume and Surface Area of a Sphere
Volume and Surface Area of a Cylinder
Volume and Surface Area of a Cone


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