Rounding and Conversion of Decimal Numbers
Primary 6 · Mathematics
Rounding and Conversion of Decimal Numbers
Lesson 1 of 5
25 min
Let's begin
At a school athletics day in Huye, the 100 m race is timed to the hundredth of a second: Ishimwe runs it in 14.68 s. At the health centre, a nurse measures medicine to the thousandth of a gram: 0.125 g. Scientists go further still, to millionths. To work with numbers like these, you first need to know what each digit after the point is worth.
| Place | As a fraction | As a decimal |
|---|---|---|
| tenths | 110 | 0.1 |
| hundredths | 1100 | 0.01 |
| thousandths | 11000 | 0.001 |
| ten-thousandths | 110000 | 0.0001 |
| hundred-thousandths | 1100000 | 0.00001 |
| millionths | 11000000 | 0.000001 |
Each place is worth ten times less than the place on its left: 1 tenth = 10 hundredths, 1 hundredth = 10 thousandths, and so on.
We read 4.752 as “four point seven five two”. You can also say “four and seven hundred fifty-two thousandths”.
Worked example 1
What is each digit of 4.752 worth?
Worked example 2
Name the place of every digit after the point in 3.140592.
So the 9 is worth 9100000 = 0.00009, and the 2 is worth 2 millionths = 0.000002.
Worked example 3
Which is bigger, 0.5 or 0.45? Write 0.5 as 0.50. Now compare 0.50 and 0.45: the tenths are 5 and 4, so 0.5 is bigger. A decimal with more digits is not always bigger!
Tip
Mirror, mirror. The ones column is the middle of the mirror. Tens ↔ tenths, hundreds ↔ hundredths, thousands ↔ thousandths. The “th” tells you the place is after the point.
Work each one in your exercise book first, then tap Show answer to check.
In 7.25613, which digit is in the ten-thousandths place?
Answer: 1. Count four places after the point.
What is the value of the 8 in 0.00082?
Answer: 8 ten-thousandths, which is 0.0008.
Write 6 + 0.3 + 0.004 + 0.0001 as one decimal.
Answer: 6.3041. There are no hundredths, so that place holds a 0.
Which is bigger, 2.089 or 2.1?
Answer: 2.1. Write it as 2.100; the tenths are 1 and 0.
What you learned today
Sources and credits
The stories, Rwandan worked examples and practice questions were written by Ganzaa.
Quick check
In 5.371942, which digit is in the hundred-thousandths place?
