1. Make and Justify Estimates

2. What is the value… -5
2.4
-0.4
2.4
0.95 ?
3.35 5 2
4.4

3. Estimating answers A farmer has 404 cows.
128 of them have been milked.
About how many are left to be milked?
Which is a better estimate:
400 – 100 = 300 or
400 – 130 = 270
Why?
Actual answer = 276

4. Estimating answers A small lawn is 7.5m by 2.5m.
Roughly what is its area?
Which is a better estimate:
7 x 3 or 8 x 3 or
7 x 2 or 8 x 2
What are the lowest and highest values?
The answer is between 7x2=14 and 8x3=24
Actual answer 7.5x2.5 = 18.75m2

5. Try estimating these ... 95 Christmas trees at £4.95 each
48 people climb the Eiffel Tower at €3.80 each
12 diskettes with 1.44Mb each
28 ambulances at £12,750
£470.25
€182.40
17.28Mb
£229,500

6. Using long multiplication
673 x 24 ≈ 700 x 20 = 14,000
673
x 24
2692 =673x4
=673x20
16152

7. Using multiplication facts
If 673 x 24 = what is:
673 x 2.4 =
6.73 x 24 =
6.73 x 2.4 =

8. Using multiplication facts
If 26 x 19 = 494 what is:
2.6 x 1.9
= 4.94
0.26 x 19
0.26 x 1.9
= 0.494