Rounding numbers rules

1. 4/27The Perfect Partner for your Digital Business
Mathematical Skills I
Rounding Rules
Pro. Ignacio Anguera
Colegio Real de Panamá

2. 4/27
Rounding means making a
number simpler but keeping
its value close to what it was.
CASE 1 – Number Greater Than 5
If the number to the right of the least significant digit is
GREATER THAN 5, round the least significant digit UP.
ROUNDING
NUMBERS RULES
Example: 123456 rounded to five significant
figures is 123460
Round the following numbers to 2 decimal places:
 4.829
 67.377
 9.896

3. 4/27
Rounding means making a
number simpler but keeping
its value close to what it was.
If the number to the right of the least significant digit is LESS
THAN 5, keep the least significant digit SAME.
ROUNDING
NUMBERS RULES
Example: 123456 rounded to three significant 123000.
CASE 2 – Number LowerThan 5
Round the following numbers to 2 decimal places:
 4.822
 67.370
 9.894

4. 4/27
Rounding means making a
number simpler but keeping
its value close to what it was.
If the number to the right of the least significant digit is
EXACTLY 5 with no nonzero digits afterward, round the
least significant digit UP if it is an ODD number; if it is EVEN,
leave it unchanged.
ROUNDING
NUMBERS RULES
Example: 12345 rounded to three significant 12340
CASE 3 – 5 Alone
Round the following numbers to 2 decimal places:
 4.825
 67.375
 9.8950000000000
Why does this rule exist?
Because if the least
significant digit is exactly 5,
we should, on average,
round the number up half
the time, and down half the
time; otherwise we risk an
accumulation of round-off
error in repeated
calculations.

5. 4/27
Rounding means making a
number simpler but keeping
its value close to what it was.
If the first figure dropped is EXACTLY 5, and there are any
figures following the five that are not zero, then round the
least significant digit UP
ROUNDING
NUMBERS RULES
Example: 123501 rounded to three significant 124000
CASE 4 – 5 And Something
Round the following numbers to 2 decimal places:
 4.8258
 67.3752
 9.89500000000003

6. 4/27
Rounding means making a
number simpler but keeping
its value close to what it was.
ROUNDING
NUMBERS RULES
Rounding Rules
More Than 5 Less Than 5 Exactly 5
digit UP digit SAME
with no nonzero
digits afterward
with any nonzero
digits afterward
digit UP
Even Odd
digit UPdigit SAME
If the first figure dropped is

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PRACTICE!
NUMBER
# of decimal
places desired
Last figure
to be kept
First figure
to be dropped
Rule
Number
becomes
6.422 1 6.4 6.42 6.4
6.4872 2
6.997 2
6.6500 1
7.485 2
6.755000 2
8.995 2
6.6501 1
7.4852007 2