Chapter 3 · Place value and decimals
Ten Times as Much and One Tenth as Much
Learn how a digit is worth ten times as much one place to the left and one tenth as much one place to the right, in whole numbers and in decimals to thousandths.
Look at the numbers and . Both use the digit , but the does not stand for the same amount in each number.
A digit is one of the ten symbols from to that you use to write numbers. A place is the position of a digit in a number, such as the ones place or the tens place. The value of a digit is the amount it stands for in its place.
In , the digit is in the ones place. It stands for ones, so its value is . In , the digit is in the tens place. It stands for tens, so its value is .
So the same digit can stand for different amounts, and its place makes the difference. In this lesson, you will find out exactly how the value changes when a digit moves one place to the left or one place to the right.
| Place of the digit 6 | Value in words | Value as a number |
|---|---|---|
thousands place | thousands | |
hundreds place | hundreds | |
tens place | tens | |
ones place | ones |
Read down the last column of the table: , , , . Then read it from the bottom up: , , , . Do you see a pattern each way?
Going up one row, the digit moves one place to the left, and its value becomes times as much. That means equal groups of the amount you had. For example, groups of make , so is times as much as .
Going down one row, the digit moves one place to the right, and its value becomes one tenth as much. One tenth, which you write as , is one of equal parts. To find of an amount, split it into equal parts and keep one part. That is the same as dividing by . For example, split into equal parts gives in each part, so is of .
The same is true for hundreds and tens. In words, is times as much as , and is of . In numbers, it looks like this:
Key concept
Each place is worth 10 times the place to its right
A digit in one place stands for times what it stands for in the place to its right. It stands for of what it stands for in the place to its left. This is true for any two places that are next to each other.
Worked example
The digit 7 in two places that are side by side
In , the digit is in the thousands place. In , the digit is in the hundreds place. How does the value of the in compare with the value of the in ?
Write what the digit 7 stands for in each number, so that you can compare the two amounts. In 7,000 it stands for 7 thousands. In 700 it stands for 7 hundreds.
The thousands place is one place to the left of the hundreds place. One place to the left means 10 times as much, so 7 thousands is 10 times as much as 7 hundreds. You can check it: 10 groups of 700 make 7,000.
Now compare in the other direction. The hundreds place is one place to the right of the thousands place. One place to the right means one tenth as much, and you find one tenth by dividing by 10.
Answer
The in stands for times as much as the in . The in stands for of what the in stands for.
The same pattern tells you how the places themselves are related. Think about what the digit stands for in each place, starting at the ones place and moving left: , , , , . Each amount is times the one before it. So it always takes of one place to make of the next place to the left:
- ones make ten.
- tens make hundred.
- hundreds make thousand.
- thousands make ten thousand.
Going the other way, hundred is of thousand, because .
You can link two of these facts to relate places that are farther apart. The next example shows how.
Worked example
From hundreds to ten thousand
How many hundreds make ten thousand?
Start at the hundreds place and move one place to the left, to the thousands place. Each place is worth 10 times the place to its right, so 10 hundreds make 1 thousand.
Move one more place to the left, to the ten thousands place. For the same reason, 10 thousands make 1 ten thousand.
Link the two facts. Ten thousand is 10 thousands, and each of those thousands is 10 hundreds. That makes 10 groups of 10 hundreds.
Check the answer. If 100 hundreds make ten thousand, then 100 groups of 100 must equal 10,000. They do.
Answer
It takes hundreds to make ten thousand.
The pattern does not stop at the ones place. Right after the ones place comes the decimal point, the dot that separates the ones place from the places for parts of . Each place after it is still worth of the place to its left.
- Tenths place. Split into equal parts. Each part is one tenth, or . You already write it as .
- Hundredths place. Split each tenth into equal parts. Now has equal parts. Each part is one hundredth, or . You already write it as .
- Thousandths place. Split each hundredth into equal parts. Now has equal parts. Each part is one thousandth, or . You write it as , with the in the third place after the decimal point.
The table below follows the digit into these places. One tenth of is tenth, so one tenth of ones is tenths.
| Place of the digit 6 | Value in words | Value as a number | Compared with one place to the left |
|---|---|---|---|
ones place | ones | is of | |
tenths place | tenths | is of | |
hundredths place | hundredths | is of | |
thousandths place | thousandths | is of |
Now read the table from the bottom up. Going up one row still moves the digit one place to the left, so each value is times as much as the value below it. This works because it takes thousandths to make hundredth, hundredths to make tenth, and tenths to make .
So is times as much as , is times as much as , and is times as much as . The digit crossed the decimal point, and the pattern stayed the same.
Worked example
One place each way from the hundredths place
Answer both questions. is times as much as what number? is of what number?
Name the value in words. In 0.04 the digit 4 is in the hundredths place, so 0.04 is 4 hundredths.
In the first question, 0.04 is 10 times as much as the other number, so the other number is one tenth of 0.04. One tenth as much means one place to the right. The 4 moves from the hundredths place to the thousandths place and stands for 4 thousandths. Zeros fill the tenths and hundredths places.
Check the first answer. It takes 10 thousandths to make 1 hundredth, so 10 groups of 4 thousandths make 4 hundredths.
In the second question, 0.04 is one tenth of the other number, so the other number is 10 times as much as 0.04. Ten times as much means one place to the left. The 4 moves from the hundredths place to the tenths place and stands for 4 tenths.
Check the second answer. It takes 10 hundredths to make 1 tenth, so 10 groups of 4 hundredths make 4 tenths. That means 4 hundredths is one tenth of 4 tenths.
Answer
The number is times as much as , and it is of .
Here is the idea to keep. A digit in any place stands for times what it would stand for one place to the right. It stands for of what it would stand for one place to the left. The same pattern links thousands and hundreds, ones and tenths, and hundredths and thousandths. The decimal point does not change it.
Next, you will compare what the same digit stands for in two places of one number, such as the digit in .