Rounding Lesson
Rounding means to make a number simpler to work with by adjusting
it up or down.
If the instructions say to round to the nearest hundred, then you will look at the number to
the right of the hundreds (in the tens place) and decided whether it should be rounded up
or down. For example, since 149 has a ‘4’ in the tens place, it will be rounded down to 100.
If 149 was being rounded to the nearest ten, then it would go up to 150.
There are several ways you can round numbers and knowing which
one to use involves critical thinking and planning ahead.
Ask yourself,



what are these numbers for?
how accurate do they need to be?
For example, at the shops you’re buying three items: $15 socks, a $67 shirt and a
$138 coat. To work out the approximate total, I leave $15 (that's easy enough to
work with), and I round $67 up to $70. Then I round $138 down to $135 to balance
rounding up before. Standard 'rules' say $138 should be rounded up to $140.
Guidelines (not rules!):
 Round up when the
number in the place to
the right is 5 or higher
 Round down when the
number to the right is 4
or lower
 Truncate* (cut off) when
there are too many
digitals to meaningfully
work with it
46
50
44
40
137.833
137
* Truncating is usually only used with decimals so that the part you cut off represents a very
small number. When working with medicines or other potentially dangerous items, do not
truncate before rounding.
Rounding to different places:
Instructions
 Round to the nearest ten (look
Original Number
Rounded
41
40
178
180
4,036
4,000
890
1,000
 Round to the nearest tenth
6.03
6.0
(look at the hundredths)
57.88
57.9
at the ones)
 Round to the nearest thousand
(look at the hundreds)
Real Life Practice:



Try to estimate the cost of your shopping as you go (e.g. bagels $4.35, milk $1.50,
paper towels $4.65, mouthwash $8.99 = $4 + $2 + $5 + $9 = $20)
Look at items in your pantry or bathroom and estimate how much of each product is
left (round to the nearest half or quarter). Then estimate how much longer it will last
(how much do you use each day?).
Estimate time: what time will you get home, to school, to work based on the time
you leave and travel time?