Rounding and Conversion of Decimal Numbers
Primary 6 · Mathematics
Rounding and Conversion of Decimal Numbers
Lesson 2 of 5
30 min
Let's begin
Mugisha's mother buys 2.36 kg of beef at the butcher in Nyamirambo. When she tells her neighbour, she says, “about 2.4 kg”. She has rounded the mass to the nearest tenth of a kilogram. How did she decide on 2.4 and not 2.3?
2.36 lies between 2.3 and 2.4. Halfway between them is 2.35. Our number, 2.36, is past halfway, so it is closer to 2.4.
“To the nearest tenth” means the same as “to 1 decimal place (1 d.p.)”. “To the nearest hundredth” means “to 2 decimal places (2 d.p.)”.
Worked example 1
Round 7.836
Worked example 2
(rounding a 9 up): Round 3.96 to the nearest tenth.
Worked example 3
Round 5.297 to the nearest hundredth. The hundredths digit is 9 and the next digit is 7, so 9 becomes 10: write 0 and carry 1 to the tenths (2 + 1 = 3). Answer 5.30.
Look at the tenths digit. 12.5 rounds up to 13. 12.49 rounds down to 12, because its tenths digit is 4. (Do not look past the tenths digit!)
Worked example 4
Ishimwe ran 100 m in 14.68 s. To the nearest tenth of a second, that is 14.7 s. A bus trip measured 45.37 km. To the nearest kilometre, that is 45 km.
Tip
Only look at your right-hand neighbour. The digit just after the rounding place decides everything. Digits further right never matter.
Work each one in your exercise book first, then tap Show answer to check.
Round 6.73 to the nearest tenth.
Answer: 6.7. The hundredths digit is 3.
Round 0.458 to 2 decimal places.
Answer: 0.46. The thousandths digit is 8, so round up.
Round 9.97 to 1 decimal place.
Answer: 10.0. 9 + 1 = 10 in the tenths, so carry into the ones.
Round 23.49 to the nearest whole number.
Answer: 23. The tenths digit is 4.
What you learned today
Sources and credits
The stories, Rwandan worked examples and practice questions were written by Ganzaa.
Quick check
Round 4.762 to the nearest tenth.
