MATHS FUNDA

Tutorial 1
Use the formula ALL FROM 9 AND THE LAST FROM 10 to perform instant subtractions.

* For example 1000 - 357 = 643
We simply take each figure in 357 from 9 and the last figure from 10.

So the answer is 1000 - 357 = 643
And thats all there is to it!
This always works for subtractions from numbers consisting of a 1 followed by noughts: 100; 1000; 10,000 etc.

* Similarly 10,000 - 1049 = 8951
* For 1000 - 83, in which we have more zeros than figures in the numbers being subtracted, we simply suppose 83 is 083.
So 1000 - 83 becomes 1000 - 083 = 917

Try some yourself:
1) 1000 - 777
=
2) 1000 - 283 =
3) 1000 - 505 =
4) 10,000 - 2345 =
5) 10000 - 9876 =
6) 10,000 - 1101 =
7) 100 - 57 =
8) 1000 - 57 =
9) 10,000 - 321 =
10) 10,000 - 38 =
Total Correct =
Tutorial 2
Using VERTICALLY AND CROSSWISE you do not need to the multiplication tables beyond 5 X 5.

* Suppose you need 8 x 7
8 is 2 below 10 and 7 is 3 below 10.
Think of it like this:

The answer is 56.
The diagram below shows how you get it.

You subtract crosswise 8-3 or 7 - 2 to get 5,
the first figure of the answer.
And you multiply vertically: 2 x 3 to get 6,
the last figure of the answer.
That's all you do:
See how far the numbers are below 10, subtract one
number's deficiency from the other number, and
multiply the deficiencies together.
* 7 x 6 = 42

Here there is a carry: the 1 in the 12 goes over to make 3 into 4.

Multply These:
1) 8
8 x


2) 9
7 x


3) 8
9 x


4) 7
7 x


5) 9
9 x


6) 6
6 x
Total Correct =
Here's how to use VERTICALLY AND CROSSWISE for multiplying numbers close to 100.

*
Suppose you want to multiply 88 by 98.
Not easy,you might think. But with
VERTICALLY AND CROSSWISE you can give
the answer immediately, using the same method
as above.
Both 88 and 98 are close to 100.
88 is 12 below 100 and 98 is 2 below 100.
You can imagine the sum set out like this:
As before the 86 comes from
subtracting crosswise: 88 - 2 = 86
(or 98 - 12 = 86: you can subtract
either way, you will always get
the same answer).
And the 24 in the answer is
just 12 x 2: you multiply vertically.
So 88 x 98 = 8624

This is so easy it is just mental arithmetic.
Try some:
1) 87
98 x


2) 88
97 x


3) 77
98 x


4) 93
96 x


5) 94
92 x


6) 64
99


7) 98
97 x

Total Correct =
Multiplying numbers just over 100.

* 103 x 104 = 10712
The answer is in two parts: 107 and 12,
107 is just 103 + 4 (or 104 + 3),
and 12 is just 3 x 4.
* Similarly 107 x 106 = 11342
107 + 6 = 113 and 7 x 6 = 42

Again, just for mental arithmetic
Try a few:
1) 102 x 107 =
1) 106 x 103 =
1) 104 x 104 =
4) 109 x 108 =
5) 101 x123 =
6) 103 x102 =
Total Correct =

Tutorial 3
The easy way to add and subtract fractions.
Use VERTICALLY AND CROSSWISE to write the answer straight down!

*
Multiply crosswise and add to get the top of the answer:
2 x 5 = 10 and 1 x 3 = 3. Then 10 + 3 = 13.
The bottom of the fraction is just 3 x 5 = 15.
You multiply the bottom number together.
So:
*
Subtracting is just as easy: multiply crosswise as before, but the subtract:
*

Try a few:






Total Correct =

Tutorial 4
A quick way to square numbers that end in 5 using the formula BY ONE MORE THAN THE ONE BEFORE.

* 752 = 5625
752 means 75 x 75.
The answer is in two parts: 56 and 25.
The last part is always 25.
The first part is the first number, 7, multiplied by the number "one more", which is 8:
so 7 x 8 = 56
* Similarly 852 = 7225 because 8 x 9 = 72.

Try these:
1) 452 =
2) 652 =
3) 952 =
4) 352 =
5) 152 =
Total Correct =
Method for multiplying numbers where the first figures are the same and the last figures add up to 10.

* 32 x 38 = 1216
Both numbers here start with 3 and the last
figures (2 and 8) add up to 10.
So we just multiply 3 by 4 (the next number up)
to get 12 for the first part of the answer.
And we multiply the last figures: 2 x 8 = 16 to
get the last part of the answer.
Diagrammatically:
* And 81 x 89 = 7209
We put 09 since we need two figures as in all the other examples.

Practise some:
1) 43 x 47 =
2) 24 x 26 =
3) 62 x 68 =
4) 17 x 13 =
5) 59 x 51 =
6) 77 x 73 =
Total Correct =

Tutorial 5
An elegant way of multiplying numbers using a simple pattern.

* 21 x 23 = 483
This is normally called long multiplication but
actually the answer can be written straight down
using the VERTICALLY AND CROSSWISE
formula.
We first put, or imagine, 23 below 21:

There are 3 steps:
a) Multiply vertically on the left: 2 x 2 = 4.
This gives the first figure of the answer.
b) Multiply crosswise and add: 2 x 3 + 1 x 2 = 8
This gives the middle figure.
c) Multiply vertically on the right: 1 x 3 = 3
This gives the last figure of the answer.

And thats all there is to it.

* Similarly 61 x 31 = 1891

* 6 x 3 = 18; 6 x 1 + 1 x 3 = 9; 1 x 1 = 1

Try these, just write down the answer:
1) 14
21 x
2) 22
31 x
3) 21
31 x
4) 21
22 x
5) 32
21 x

Total Correct =
Multiply any 2-figure numbers together by mere mental arithmetic!
If you want 21 stamps at 26 pence each you can
easily find the total price in your head.
There were no carries in the method given above.
However, there only involve one small extra step.

* 21 x 26 = 546

The method is the same as above
except that we get a 2-figure number, 14, in the
middle step, so the 1 is carried over to the left
(4 becomes 5).

So 21 stamps cost ?5.46.
Practise a few:
1) 21
47 x
2) 23
43 x
3) 32
53 x
4) 42
32 x
5) 71
72 x

Total Correct =

* 33 x 44 = 1452
There may be more than one carry in a sum:

Vertically on the left we get 12.
Crosswise gives us 24, so we carry 2 to the left
and mentally get 144.
Then vertically on the right we get 12 and the 1
here is carried over to the 144 to make 1452.

6) 32
56 x
7) 32
54 x
8) 31
72 x
9) 44
53 x
10) 54
64 x

Total Correct =
Any two numbers, no matter how big, can be
multiplied in one line by this method.
Tutorial 6
Multiplying a number by 11.

To multiply any 2-figure number by 11 we just put
the total of the two figures between the 2 figures.
* 26 x 11 = 286
Notice that the outer figures in 286 are the 26
being multiplied.
And the middle figure is just 2 and 6 added up.
* So 72 x 11 = 792

Multiply by 11:
1) 43 =
2) 81 =
3) 15 =
4) 44 =
5) 11 =
Total Correct =

* 77 x 11 = 847
This involves a carry figure because 7 + 7 = 14
we get 77 x 11 = 7147 = 847.

Multiply by 11:
1) 88 =
2) 84 =
3) 48 =
4) 73 =
5) 56 =
Total Correct =

* 234 x 11 = 2574
We put the 2 and the 4 at the ends.
We add the first pair 2 + 3 = 5.
and we add the last pair: 3 + 4 = 7.

Multiply by 11:
1) 151 =
2) 527 =
3) 333 =
4) 714 =
5) 909 =
Total Correct =

Tutorial 7
Method for diving by 9.

* 23 / 9 = 2 remainder 5
The first figure of 23 is 2, and this is the answer.
The remainder is just 2 and 3 added up!
* 43 / 9 = 4 remainder 7
The first figure 4 is the answer
and 4 + 3 = 7 is the remainder - could it be easier?

Divide by 9:
1) 61 = remainder
2) 33 = remainder
3) 44 = remainder
4) 53 = remainder
5) 80 = remainder
Total Correct =

* 134 / 9 = 14 remainder 8
The answer consists of 1,4 and 8.
1 is just the first figure of 134.
4 is the total of the first two figures 1+ 3 = 4,
and 8 is the total of all three figures 1+ 3 + 4 = 8.

Divide by 9:
6) 232 = remainder
7) 151 = remainder
8) 303 = remainder
9) 212 = remainder
10) 2121 = remainder
Total Correct =

* 842 / 9 = 812 remainder 14 = 92 remainder 14
Actually a remainder of 9 or more is not usually
permitted because we are trying to find how
many 9's there are in 842.
Since the remainder, 14 has one more 9 with 5
left over the final answer will be 93 remainder 5

Divide these by 9:
1) 771 = remainder
2) 942 = remainder
3) 565 = remainder
4) 555 = remainder
5) 777 = remainder
6) 2382 = remainder
7) 7070 = remainder
Total Correct =