NUMBERS • ROUNDING 27
Rounding to different place values
Rounding to different place values will give us
different results. Let’s look at what happens to 7641
when we round it to different place values.
Rounding to significant digits
We can also round numbers to one or
more significant digits.
Estimating height
This robot is 165 cm tall.
TRY IT OUT
What is his height rounded
to the nearest 10 cm?
What is his height rounded
to one significant digit?
(See below.)
Answers on page 319
165 cm
The rounded number
is very close to the
original
7 6 4 1
7 6 4 0
7 6 0 0
ROUNDED TO THE 8 0 0 0
NEAREST 1000
Let’s look at the number 6346. The
most significant digit is the one with
the highest place value. So, 6 is the most
significant digit. The digit after it is less
than 5, so we round down to 6000.
The second significant digit is in the
hundreds. The next digit is less
than 5, so when we round to two
significant digits, 6346 becomes 6300.
The third significant digit is in
the tens column. If we round our
number to three significant digits, it
becomes 6350.
The higher the place
value we round to, the
more different the
result could be to the
original number
6 3 4 6
6 3 4 6
6 3 4 6
6 0 0 0
6 3 0 0
6 3 5 0
ROUNDED TO ONE
SIGNIFICANT DIGIT
ROUNDED TO TWO
SIGNIFICANT DIGITS
ROUNDED TO THREE
SIGNIFICANT DIGITS
In a four-digit number, rounding to the
most significant digit is the same as
rounding to the nearest 1000
This is the second
significant digit
We round using
this digit
We round with
this digit
This is the third
significant digit
ROUNDED TO THE
NEAREST 100
ROUNDED TO THE
NEAREST 10
ORIGINAL NUMBER
We use this
digit when
rounding
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