Multiplying Decimals

Multiply in three steps. First ignore the decimal points and multiply the digits as whole numbers, so 0.34 × 2.5 becomes 34 × 25 = 850. Next count the decimal places in both numbers, which is 3 in total. Finally move the point 3 places left to get 0.85.

Counting the decimal places tells you how far to move the decimal point in the answer. You add the decimal places in both numbers. For 0.34 × 2.5 that is 2 plus 1, giving 3 places, so the point moves 3 places left and the answer stays the right size.

First multiply the digits as whole numbers, then move the decimal point to the left in that product. Move it by the total number of decimal places in the original numbers. For 34 × 25 = 850 with 3 decimal places, the point moves 3 places left to give 0.85.

You can multiply decimals by hand because the method only uses whole-number multiplication. Ignore the decimal points and multiply the digits, count the total decimal places, then move the point left by that many places. So 0.34 × 2.5 becomes 34 × 25 = 850, then 0.85.

Multiply the rate by the quantity using the decimal method. A taxi at 6.5 pounds per kilometre for 8.12 kilometres costs 6.5 × 8.12. Multiply 65 × 812 = 52780, count 3 decimal places in total, then move the point 3 places left to get 52.78 pounds.