Transcript Rounding and Estimating

Rounding and Estimating
Create a magic number square
This is where every row, column and diagonal add up
to the same total.
Eg
11
3
10
7
6
8
13
9
5
Now design your own to add up to 28 and if you do
that try 32.
To get you mind working..
Brain Gym time!!
Objectives for today
By the end of the session you will:

Approximate numbers to,
1.
2.
3.

the nearest 10, 100
1 and 2 decimal places
1 and 2 significant figures
Use estimation for size and to check
working out.
In groups of 2 or 3, decide what the
following mean and what is involved in
doing it.
You have 5 minutes to get your ideas
down on paper.
1.
2.
3.
Approximating
Rounding
Estimating
Findings…..
Approximating
Rounding
Estimating
Why do we need to be able to
approximate and estimate?


Sometimes we only need an
approximate answer to a problem or
question.
We do not need to be always exact.
Working in 2s or 3s.
Look at the information on the sheet.
You have 10 minutes to create a quick
poster to say,
What the main rule for rounding is.
What you do to round to,
The nearest ten and a hundred
To 2 decimal places
To 2 significant figures
Examples
Rounding 27 to the nearest ten - Answer 30
Rounding 357 to the nearest hundred – Answer 400
Rounding 2.634 is 2 decimal places - Answer 2.63
Rounding 34.265 to 2 decimal places – Answer 34.27
Rounding 35.54 to 2 significant figures -Answer 36
Rounding 0.0455 to 2 significant figures - Answer 0.046
Findings - Recap
Main rule – Look at the figure to the right
of where you are rounding to.
If this number is,
0 to 4 – eg 454 becomes 450
5 to 9 – eg 457 becomes 460
Findings Recap– To the nearest
10, hundred and thousand
If to 10, your answer should have no decimal
points and should end in one zero
eg 19 = 20
If to 100, as above but should end in 2 zeros
eg 805 = 800
It to 1000, as above but should end in 3 zeros
Eg 8950 = 9000
Findings recap - Decimal
places and significant figures
2 Decimal places
We need two numbers after the decimal point,
look at the 3rd number and use the main rule.
Eg 36.5823 is 36.58
2 Significant Figures
Count all the numbers not just the ones after
the decimal point. Always count the numbers
from the left.
Eg 16.045 is 16
You have 10 minutes to
answer the questions.
Using estimation to check
results and quantities
Am I bothered????????????????
You should be,
it’s very useful as it can help you spot mistakes
and
you will need it in your assignment.
Things to help you estimate
Use your white board for your answer

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30 cm or 12 inches is the length of a
ruler
A bag of sugar is 1 kilo or about 2lbs
1/2 litre or 500ml is a small bottle of
water
Spotting errors – checking your work
Using rounding and estimating together!
Round the numbers to 1 significant figure and
then say if you think the answer is right or
wrong. RECAP SIG FIGS
 8.67 x 51.9 = 44.9973
 33.29 x 3.2 = 106.528
 521 divided by 97.6 = 0.5338
 7.4 x 4.2 x 0.95 = 29.526
Recap of work and objectives
By the end of the session you will have:

Approximated numbers to,
1.
2.
3.



the nearest 10, 100
1 and 2 decimal places
1 and 2 significant figures
Used estimation for size and to check working out.
Homework – Try it when you are out and spend
money, check roughly by estimation. Are you being
charged the right amount?
Now mark up your progress card and hand your
work in.