Transcript Approximation Estimation

CHAPTER 3
Approximation and Estimation
ROUNDING TO A GIVEN
NUMBER OF DECIMAL PLACES
When you round a decimal number to a specified
number of DECIMAL PLACES (d.p) you must look at the
digit after the decimal place that you want, if this digit is:
 Less than 5, the decimal place you want is left as it is
e.g. 84.2461 rounded to 3 d.p
= 84.246 to 3 d.p
 5 or more, the decimal place you want is increased by 1
e.g. 84.2461 rounded to 2 d.p
= 84.25
to 2 d.p

ROUNDING TO A NUMBER OF SIGNIFICANT
FIGURES

In any number the first SIGNIFICANT FIGURE (sf) is the first digit which is
not a zero, for example, for these numbers the first SIGNIFICANT FIGURE
is in red
32.5
423
56.89
0.92
To round to a specified number of SIGNIFICANT FIGURES you must look
at the digit after the required number of SIGNIFICANT FIGURES if this digit
is:
(a) Less than 5, the specified number of significant figures are left as they are
and any other digits to the left of the decimal point are changed to zero
Eg
224 138 is
220 000
to
2 sf
224 138 is
224 100
to
4 sf
(b) 5 or more, the last significant figure is increased by 1 and any other digits to
the left of the decimal point are changed to zero
Eg
45.79
is
50
to
1 sf
45.79
is
45.8
to
3 sf


Note: The answer to a calculation should never have more significant
figures than the numbers in the question.