Rounding and Conversion of Decimal Numbers
Primary 6 · Mathematics
Rounding and Conversion of Decimal Numbers
Lesson 5 of 5
30 min
Let's begin
At the market, Habimana sees groundnuts sold in 38 kg bags and sugar sold in 0.4 kg bags. “Which bag is heavier?” he wonders. To compare them, he needs both amounts in the same form.
Worked example 1
0.6 → the last digit is in the tenths → 610 → divide by 2 → 35.
Worked example 2
0.45 → hundredths → 45100 → GCF(45, 100) = 5 → 920.
Worked example 3
0.125 → thousandths → 1251000 → GCF = 125 → 18.
Worked example 4
2.75 → 2 and 75 hundredths → 2 75100 → simplify 75100 by 25 → 2 34.
Worked example 5
0.008 → thousandths → 81000 → divide by 8 → 1125.
Worked example 6
(comparing): Habimana's bags. Change 38 into a decimal: 3 ÷ 8 = 0.375. Compare 0.375 and 0.400: the tenths are 3 and 4. So the 0.4 kg bag of sugar is heavier.
Worked example 7
(ordering): Put 0.6, 58, 1320 and 0.61 in order from smallest to biggest.
Worked example 8
(what is left): Keza drank 0.35 L from a 1 L packet of milk. What fraction of a litre is left?
Tip
Say it, then write it. Read 0.45 aloud as “forty-five hundredths” and you have already written 45100. Then simplify.
Work each one in your exercise book first, then tap Show answer to check.
Write 0.8 as a fraction in simplest form.
Answer: 810 = 45.
Write 0.36 as a fraction in simplest form.
Answer: 36100 = 925.
Write 3.2 as a mixed number.
Answer: 3 210 = 3 15.
Write 0.075 as a fraction in simplest form.
Answer: 751000 = 340.
Which is bigger, 720 or 0.3?
Answer: 720 = 0.35, which is bigger than 0.30.
What you learned today
Sources and credits
The stories, Rwandan worked examples and practice questions were written by Ganzaa.
Quick check
Write 0.85 as a fraction in its simplest form.
