Learning Objectives
- Understand decimal numbers (tenths and hundredths)
- Relate decimals to fractions
- Read and write decimal numbers
- Use decimals in money and measurement
Key Concepts
What are Decimals?
A decimal number uses a dot (decimal point) to show parts of a whole. The first digit after the dot shows tenths, and the second digit shows hundredths. For example, 2.5 means 2 and 5 tenths (2 whole things and half of another). The number 3.75 means 3 and 75 hundredths.
Tenths
When you divide something into 10 equal parts, each part is one-tenth (1/10 = 0.1). If you divide a chocolate bar into 10 pieces and eat 3, you have eaten 3/10 = 0.3 of the bar. Tenths are the first place after the decimal point. 0.1, 0.2, 0.3... up to 0.9, and then 1.0 (which is a whole).
Hundredths
When you divide something into 100 equal parts, each part is one-hundredth (1/100 = 0.01). Money uses hundredths: Rs 5.50 means 5 rupees and 50 hundredths of a rupee (50 paise). A ruler shows centimetres, and each cm is 1/100 of a metre, so 1 cm = 0.01 m. Hundredths are the second place after the decimal point.
Decimals in Daily Life
We use decimals every day! Money: Rs 12.75 (12 rupees and 75 paise). Length: 1.5 m (one and a half metres). Weight: 2.25 kg (two and a quarter kilograms). Temperature: 37.5 degrees (body temperature). Decimals help us express values more precisely than whole numbers alone.
Important Terms
- Decimal Point: The dot that separates the whole number part from the fractional part
- Tenths: The first place to the right of the decimal point (1/10 = 0.1)
- Hundredths: The second place to the right of the decimal point (1/100 = 0.01)
- Decimal Number: A number written using a decimal point
- Place Value: The value of a digit based on its position
Quick Revision
- Decimals show parts of a whole using a dot
- 1/10 = 0.1 (one tenth), 1/100 = 0.01 (one hundredth)
- Rs 5.50 = 5 rupees and 50 paise
- 1.5 m = 1 metre and 50 centimetres
- The first digit after the dot is tenths; the second is hundredths
- 0.5 = 1/2 = 50/100