Hints and Things does not use any 1st Party cookies - more information .
Handy shortcuts for checking calculations, without the need of a calculator!
To check addition is correct -
To check subtraction is correct:-
To check multiplication is correct:-
To check division is correct:-
If two columns of figures should balance but don't, subtract one total from the other and if the difference is 1, 10, 100, 9 or 99 you have probably made an error in addition.
If the difference is divisible by 9 you have probably transposed a figure (e.g. written 89 instead of 98).
This was also sent in by KB who gave the following illustration -
If your balance says 45.25 but your statement says 42.55 - the difference is 2.70 which is divisible by 9 so, therefore, it is probably a transposed figure. You can see the 5 and 2 have been transposed.
To "square" a number (i.e. multiply a number by itself e.g. 17 x 17)
Example A - 17 x 17
Example B - 52 x 52
This shortcut was sent in by Sue Knight - thanks.
An easy way to remember your nine times table is -
a: The figures in the answer always total 9
2 x 9 = 18 (1+8 =
b: Deduct 1 from the number you are multiplying and the second number in the answer then becomes obvious (as it must total 9).
To multiply 8 x 9
Deduct 1 from the 8 = 7 (this is the first number of the answer)
The numbers in the answer always total 9 so the second number must be 2
Therefore 8 x 9 =72
Now for the 11 times table -
a: Add together the digits you are multiplying e.g. 33 x 11 add the 3 + 3 =6
b: Place the the answer in between the two digits e.g. 363
Therefore 33 x 11 = 363
If the two digits add up to more than ten (e.g. 48 x 11 where 4+8=12) then you have to add the 1 to the 4 and place the 2 in the middle of the two numbers.
Therefore 48 x 11 = 528
If you ever need to find out the sum of all the numbers between two given digits, here is the formula :-
ADD TOGETHER THE FIRST NUMBER AND THE LAST NUMBER IN THE SEQUENCE THEN MULTIPLY BY THE NUMBER OF THE MIDDLE NUMBER IN THE SEQUENCE.
I will try to explain - say you wanted to find out the total of numbers 7 through to 35.
i.e. 7+8+9 +10+11 an so on until..33+34+35.
First add the first number in the sequence to the last number in the sequence, which in this case is - 7 + 35 = 42
Then to find the NUMBER of the middle digit in the sequence you deduct the lowest number from the highest number, add 1 then divide by 2
i.e. 35 - 7 = 28 + 1 = 29 divided by 2 =14.5
NOW MULTIPLY 42 X 14.5 = 609
SO THE SUM OF ALL FIGURES BETWEEN 7 AND 35 = 609
Now all you accountants out there - give us some more (or have you forgotten them!) - contact us on firstname.lastname@example.org.
For more mathematical shortcuts click here.
Copyright © 2000-2014 Hints and Things
Hints and Things cannot be held responsible for any information given on this site nor do they necessarily agree with, or endorse, the views given by third parties.