Adding and Subtracting Decimals
Decimal number
- A decimal number is a fraction whose denominator is a power of 10. For example, the fraction 4⁄10 can be written in decimal form as 0.4, where:
- The dot is called the decimal point.
- The number to the right of the decimal point denotes the numerator of the fraction, that is, the fractional part.
- The number to the left of the decimal point denotes the whole number part of the fraction.
- For example, 4 3⁄10 is expressed as 4.3, where 4 is the whole number part and 0.3 is the fractional part.
- The decimal point separates the whole number part from the fractional part.
Decimals in Real Life
We deal with decimal addition and subtraction in everyday life while dealing with:
- Money
- Measurements (Length, Mass, Capacity)
- Temperature
Decimals can be added or subtracted in the same way as we add or subtract whole numbers.
Steps to Add or Subtract Decimals
- Convert decimals to like decimals. (Decimals that have the same number of digits after the decimal point are like decimals).
- Write the decimals one below the other as per the places of the digits.
- Add or subtract starting from the rightmost digit and moving towards the leftmost digit.
- Place the decimal point under the decimal point in the answer.
Example: Add 23.45; 13.101 and 345.5
1. Convert to like decimals: The highest decimal place is 3, so we add zeros in other numbers and get 3 decimal places in them too.
13.101
23.45 = 23.450 345.5 = 345.500
2. Line up the decimals:
3. Add:
4. Place decimal in answer:
Example: Kylie had 25 m of ribbon. She uses 8 m and 13 cm to decorate a skirt. How much ribbon is remaining with Kylie?
Solution:
Length of ribbon Kylie had = 25 m = 25.00
Length of ribbon used by Kylie = 8 m 13 cm = 8.13
The remaining length of ribbon = 25.00 – 8.13
= 16.87
| Fun Facts – The word “decimal” originated in the early 17th century from the Latin word “Decimus” which means “tenth”. – We use decimals when we want precise and accurate answers. |
