Decimals and Percentages

Decimals and percentages are ways of writing parts of a whole — just like fractions. In this lesson you will learn how they work, how to calculate with them, and how fractions, decimals, and percentages are all connected.

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Understanding Decimals

A decimal number uses a decimal point to separate the whole number part from the fractional part.

Ones	.	Tenths	Hundredths	Thousandths
3	.	4	5	6

This number is 3.456:

• 3 is the ones part
• 4 tenths = 4/10
• 5 hundredths = 5/100
• 6 thousandths = 6/1000

So 3.456 = 3 + 4/10 + 5/100 + 6/1000.

Comparing decimals: Always compare digit by digit from left to right.

• 0.42 vs 0.4: 0.42 has 4 tenths and 2 hundredths; 0.4 has only 4 tenths. So 0.42 > 0.4.
• Do not be fooled by length: 0.9 > 0.35 (9 tenths is more than 3 tenths).

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Multiplying and Dividing by 10, 100, 1000

When you multiply by 10, each digit moves one place to the left (the number gets 10 times bigger).