Decimals
A decimal is just a whole number with its place values shifted: 3.75 is 3 ones, 7 tenths and 5 hundredths. Keep track of place value and decimals behave exactly like the whole numbers you already know.
Three lessons cover the essentials: moving the point when you multiply or divide by 10, 100 and 1,000; adding and subtracting with the points lined up; and multiplying decimals by working with whole numbers and putting the point back at the end.
Multiplying and Dividing Decimals by 10, 100 and 1,000
Count the zeros and move the decimal point that many places: right to multiply (3.7 × 10 = 37), left to divide (4.5 ÷ 10 = 0.45).
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Method 2 · Level 1Adding and Subtracting Decimals
Line up the decimal points, fill gaps with zeros, then add or subtract as with whole numbers: 2.5 + 1.75 = 2.50 + 1.75 = 4.25.
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Method 3 · Level 2How to Multiply Decimals
Ignore the points, multiply the whole numbers, then give the answer as many decimal places as the two numbers have together: 0.3 × 0.4 → 3 × 4 = 12 → 0.12.
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