Page 36 - Mathematics Coursebook

3.3 Ordering decimals

3.3 Ordering decimals

To order decimal numbers you must write them in order of size, from the smallest to the largest.
Different whole-number parts
First compare the whole-number part of the numbers.

Look at these three decimal numbers. 8.9, 14.639, 6.45
If you highlight just the whole-number parts you get: 8.9, 14.639, 6.45
Now you can see that 14 is the biggest and 6 is the smallest of the whole numbers.
So, in order of size, the numbers are: 6.45, 8.9, 14.639

Same whole-number parts

When you have to put in order numbers with the same whole-number part, you must 'rst compare the
tenths, then the hundredths, and so on.
Look at these three decimal numbers. 2.82, 2.6, 2.816
!ey all have the same whole number of 2. 2.82, 2.6, 2.816

If you highlight just the tenths you get: 2.82, 2.6, 2.816
Now you can see that 2.6 is the smallest, but the other
two both have 8 tenths, so highlight the hundredths. 2.6, 2.82, 2.816 Put the 2.6 at the start

You can now see that 2.816 is smaller than 2.82. as you now know it’s
the smallest number.
So, in order of size, the numbers are: 2.6, 2.816, 2.82

Worked example 3.3

Write the decimal numbers in each set in order of size.
a 6.8, 4.23, 7.811, 0.77 b 4.66, 4.6, 4.08

a 0.77, 4.23, 6.8, 7.811 All these numbers have a different whole-number part, so you don’t need to
compare the decimal part. Simply write them in order of their whole-number
parts, which are 0, 4, 6 and 7.
b 4.08, 4.6, 4.66 All these numbers have the same whole-number part, so start by comparing
the tenths. 4.08 comes fi rst as it has the smallest number of tenths (zero
tenths). 4.6 and 4.66 have the same number of tenths, so compare the
hundredths. 4.6 is the same as 4.60 so it has 0 hundredths. 4.6 comes
before 4.66 which has 6 hundredths.

) Exercise 3.3

1 Write down which is the smaller decimal number from each pair.
a 13.5, 9.99 b 4.32, 3.67 c 12.56, 21.652
d 127.06, 246.9 e 0.67, 0.72 f 3.4, 3.21
g 18.54, 18.45 h 0.05, 0.043 i 0.09, 0.1
2 Write these decimal numbers in order of size, starting with the smallest.
a 3.46, 2.6, 3.31, 3.49 b 0.71, 0.52, 0.77, 0.59 c 6.9, 6.82, 6.8, 6.97
d 5.212, 5.2, 5.219, 5.199 e 32.448, 32.42, 32.441, 32.4 f 9.08, 9.7, 9.901, 9.03, 9.99
3 Place value, ordering and rounding 35