Adding and Subtracting Decimals
We usually add numbers when we have different and varied data, but when we are given with a set of repeated data, we multiply.
Multiplication is a much easier way to calculate repeated data.
2 × 3 also means 2 + 2 + 2 which is equal to 6.
Example: Let’s say Jim buys 4 pens costing $3.50 each. What is the total cost?
Cost of one pen = $3.50 3.50
Hence, the cost of 4 pens = $3.50 × 4 + 3.50
Why is place value important when adding and subtracting decimals?
Let’s look at this example now: 2.87 + 3.02 + 0.006 + 123.9 + 4
Example: Renée bought 6.75 pounds apples, 4.5 pounds oranges, 3.82 pounds bananas and 2.25 pounds grapes. How much of fruits did she buy in all?
Solution: Fruits Renée bought in all = 6.75 + 4.5 + 3.82 + 2.25 = 17.32 pounds
How do you subtract with decimals?
Subtracting decimals is much similar to the way we have learnt above in adding decimals. Let’s see how.
Example: Daniel has 2 pieces of wood measuring, 10.34 inches and 7.56 inches. How much longer is the first piece than the second one?
Subtract the lengths of 2 given wooden pieces. 10.34
So, the first piece is 2.78 inches longer than the second wooden piece.
Add the following decimals:
- 3.25 + 1.32 + 4.67
- 1.46 + 2.35 + 1.00
Subtract the following decimals:
- 5.82 – 1.23
- Richard has 100.56 pounds of grain out of which he 34.156 pounds to his brother, John. How many pounds of grain is Richard left with?
- A box of peanut butter cookies cost $3.40 and a box of oatmeal cookies cost $4.25. What is the total cost for both cookies boxes?
- Mary has 20.752 inches of ribbon out of which she used 12.456 inches of ribbon for decorating purpose. How much ribbon is she left with?
- 66.404 pounds
- 8.296 inches
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