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Just looked at 87 X 99 =
In one's mind, subtract the 87 from 100 =13
subtract the 99 from 100 = 1
13x1 = 13 = Last two digits of the problem.
Subtract diagonally the 13 from 99 = 86
the 1 from 87 = 86
86 is the first two digits of the result.
8613
~~~~~~~~~~~~~~~~~
The problem is, why can't I do the same thing with ?
82 X 88 and others - what's wrong with maths that it's not consistent ?
What am I missing here please, it's driving me round the bend ?
Yes, thanks very much Jane - The very reason
I included 'Elementary,' and 'Simple,' was to give the impression I was looking for 'E' and 'S,' rather than X or Y Algebraic equations.
The example I gave can be worked out as a mental ex., and many other such numbers can be multiplied just as easily, but unfortunately not all can be carried out in the same way - I want to use the same basic method as my example, but need to know how to do it regardless of the two numbers.
As you know how to do it algebraically, then that must mean you have the capacity to do it via the simple method - the latter is all I need.
Kind Regards.
On some of the workouts this works, but on others not - well, not quite in the same way - can someone please advise on any very simple
' how to ' formulas to get the
same result regardless of the numbers involved ?
Example,
91 X 92 =
= 9 =8
Subtract the 91 from 100 = 9
X
Subtract the 92 from 100 = 8 = 72 is the last two digits of the result.
Subtract Diagonally,the 9 from 91= 83
" " ,the 8 from 92= 83 so 83 is the first two digits of the result.
Result of 91X 92 = 8372
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