Transcript L.O.1 To be able to use known facts and place value to multiply and divide mentally.

L.O.1
To be able to use known facts and place
value to multiply and divide mentally
0
We are going to count in steps of 0.6
0.6 x 1 = 0.6
0.6 x 2 = 1.2
0.6 x 3 = 1.8
0.6 x 4 = 2.4
6x1=6
6 x 2 = 12
6 x 3 = 18
6 x 4 = 24
NOTICE that 0.6 is ten times smaller than 6
Q. What is 0.6 x 9?
The answer will be 10 times smaller than 6 x 9
We will do some
RAPID
MENTAL
CALCULATIONS
using 0.6 and 6
L.O.2
To be able to extend written methods to
multiplication of HTU x U and U.t x U
258 x 9
Estimate = 258 x 10 = 2580
BUT
this will be “out” by 258.
Estimates made when multiplying are often not
as close as those done when adding or subtracting.
Q. If 258 x 10 = 2580 how else could we have calculated
258 x 9?
x
258
9
1800
450
72
2322
Q. Where do you think 1800, 450, 72 and 2322 have
come from?
x
258
9
1800
450
72
2322
It’s easy really!
=
200 x 9
=
50 x 9
=
8 x 9
= 1800 + 450+ 72
Look at this one:
473 x 9
x
473
9
3600
630
27
4257
Look at this one:
473 x 9
x
473
9
3600
630
27
4257
=
400 x 9
=
70 x 9
=
3x9
= 3600 + 630 + 27
Try these.
Use BOTH layouts for the first three
and your preferred layout for the last two.
Remember to approximate first.
254 x 6
378 x 9
254 x 5
872 x 9
746 x 6
LOOK…
x
258
9
18
45
72
135
Q. Can the answer possibly be right?
What is wrong?
Here the answer
figures are in
the wrong place.
x
258
9
18
45
72
135
Here the answer
figures are in
the right place.
x
258
9
18 - 45 72
2322
The PLACE VALUE of the figures is VITAL.
Yesterday we did 5.7 x 6
How could we lay this out vertically as we
did for some of our calculations today?
We need to think carefully about where the
figures go ….. PLACE VALUE
x
5.7
6
30
4.2
34.2
Here we need to ALIGN the DECIMAL POINTS
By the and of the lesson the children
should be able to:
Develop an efficient standard method that
can be applied generally, approximating
first.