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Rounding to Significant Figures
Objectives: Round off numbers to a
given number of significant figures
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In real life, there are only a few occasions
when you will have to work things out
exactly. Most of the time, you will need to
work things out sensibly.
In your exams, you will be asked to give
answers to a certain number of significant
figures (s.f.). The following slides will help
you to do this correctly.
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Rounding to a Required Number of
Significant Figures (s.f.)
We use a calculator
and its display gives
the answer
39.93055556…
We need to be
able to round off
39.93055556
to 3 s.f.
Here is how
to do it…
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39.93055556… to 3 s.f.
Is this a 5
or bigger?
Look at the
4th figure
Because the
answer is NO, we
write the first
three significant
figures like this…
No
39.9
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Rounding to a Required Number of
Significant Figures (s.f.)
2. To 3
signifi
cant f
evalua
igures
te
72.4 x
14.6 ÷
23.1
We use a calculator
and its display gives
the answer
45.75930736…
We need to be
able to round
off
45.75930736
to 3 s.f.
÷
Here is how
to do it…
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45.75930736 … to 3 s.f.
Is this a 5
or bigger?
Look at the
4th figure
Because the answer
is YES, we write the
first three
significant figures
making the digit one
larger like this…
Yes
45.8
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Rounding to a Required Number of
Significant Figures (s.f.)
3. There are 67 coaches in the
coach park at a theme park. If
each coach can carry 52 passengers, calculate to 2 significant
figures the number of people
that the coaches could have
brought to the theme park.
We need to be
able to round off
to 3484 to 2 s.f.
We use a calculator and
its display gives the
answer
67 x 52 = 3484
Here is how
to do it…
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3484 to 2 s.f.
Yes
Is this a 5
or bigger?
Look at
the 3rd
figure
Because the answer
is YES, we write the
first two significant
figures making the
digit one larger like
this…
3500
Remember to
write in noughts
for the figures
after the second
digit
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Rounding to a Required Number of
Significant Figures (s.f.)
We use a calculator
and its display gives
the answer
0.021661721…
We need to be
able to round off
to 0.021661721…
to 2 s.f.
Here is how
to do it…
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0.021661721 to 2 s.f.
Is this a 5
or bigger?
Look at this
3rd figure
Because the
answer is YES, we
write the first two
significant figures
making the digit
one larger like
this…
Yes
0.022
Remember to
write in nought
before the
significant figures
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Round off the given significant figures
1.
2.
3.
4.
5.
6.
7.
8.
9.
1256
1256
1256
2359
2359
2359
79813
79813
79813
to
to
to
to
to
to
to
to
to
2 sf
1sf
3 sf
2 sf
1sf
3 sf
2 sf
1sf
3 sf
11.
12.
13.
14.
15.
16.
17.
18.
19.
10.
79813 to 4 sf
20.
25.45
25.45
25.45
0.03125
0.03125
0.03125
12.056
12.056
12.056
to
to
to
to
to
to
to
to
to
2 sf
1sf
3 sf
2 sf
1sf
3 sf
2 sf
1sf
3 sf
12.056 to 4 sf
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Round off the given significant figures
1.
2.
3.
4.
5.
6.
7.
8.
9.
1256
1256
1256
2359
2359
2359
79813
79813
79813
 1300
 1000
 1260
 2400
 2000
 2360
 80000
 80000
 79800
11.
12.
13.
14.
15.
16.
17.
18.
19.
10.
79813  79810
20.
25.45
25.45
25.45
0.03125
0.03125
0.03125
12.056
12.056
12.056
 25
 30
 25.5
 0.031
 0.03
 0.0313
 12
 10
 12.1
12.056  12.06
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