Rounding and Conversion of Decimal Numbers
Primary 6 · Mathematics
Rounding and Conversion of Decimal Numbers
Lesson 4 of 5
30 min
Let's begin
A recipe from Keza's grandmother says “34 of a litre of milk”, but Keza's measuring jug is marked in decimals: 0.25 L, 0.5 L, 0.75 L, 1 L. Which mark should she fill to? She needs to turn a fraction into a decimal.
Tenths, hundredths and thousandths can be written straight away:
Multiply the top and bottom by the same number so that the denominator becomes 10, 100 or 1000.
A fraction is a division: 78 means 7 ÷ 8. Write 7 as 7.000 and divide.
For a mixed number, convert the fraction part and keep the whole number: 2 34 = 2 + 0.75 = 2.75.
Try 2 ÷ 3: 20 ÷ 3 = 6 remainder 2, then 20 ÷ 3 = 6 remainder 2 again … The 6 repeats forever: 23 = 0.666… This is called a recurring decimal. We round it:
| Fraction | 12 | 14 | 34 | 15 | 18 | 110 |
|---|---|---|---|---|---|---|
| Decimal | 0.5 | 0.25 | 0.75 | 0.2 | 0.125 | 0.1 |
Tip
The fraction bar is a division sign. If you cannot quickly make the bottom 10, 100 or 1000, just divide the top by the bottom.
Work each one in your exercise book first, then tap Show answer to check.
Write 425 as a decimal.
Answer: 16100 = 0.16.
Write 720 as a decimal.
Answer: 35100 = 0.35.
Write 58 as a decimal.
Answer: 0.625 (5 ÷ 8).
Write 3 15 as a decimal.
Answer: 3 + 0.2 = 3.2.
Write 56 as a decimal rounded to 2 decimal places.
Answer: 5 ÷ 6 = 0.8333…, so 0.83.
What you learned today
Sources and credits
The stories, Rwandan worked examples and practice questions were written by Ganzaa.
Quick check
Match each fraction to its decimal.
Tap one on the left, then its partner on the right.
