Adding and Subtracting Decimals
When we add or subtract decimal numbers, we obtain a decimal number. What technique should we use when we cannot use a calculator?
I. The numbers are written with the same number of decimal places
We just need to place the digits of the same place values in the same columns.
We correctly line up the digits of the whole numbers. Then, to the right of the decimal point, we place the digits for the tenths under one another, and so on for the hundredths and the other decimals.
Then we can carry out the addition using the normal technique.
II. The numbers are not written with the same number of decimal places
It is always possible to write the decimal numbers with the same number of decimal places by adding zeros to the right of the decimal point.
Thus, 59.8 – 2.934 = 59.800 – 2.934. By laying out the numbers in the same way as before.
Borrow 10 from the digit on the left.
Then we can carry out the subtraction using the normal technique.
Adding and Subtracting Decimals - Interactive PowerPoint lesson