math shortcuts?

Question

I saw on the news last night about a guy who had shortcuts for math, ex. 35X35=1225 take the 3 times one up so 3X4=12 and 5X5=25 to make 1225 do you know any more?

Answer 1

Here are few...


Whenever you are multiplying any number by 11....

xy x 11 = x(x+y)y

e.g. 21 x 11 = 231 Thats it. If there are carry over value of x will have to be adjusted accrodingly but you can still do this in your head.

e.g. 57 x 11 = 627 (7+5=12) Put 2 in middle and carry ove 1 to 5 and make it 6.

128 x 11 = 1408 (The 4 and 0 comes form addition of 8+2 = 10 and 2+1 = 3 and you must make 3 into 4 carry over 1 of 10. etc...


mutliplying 2 digits...

6 x 9 = ?


6 4

9 1
_____
5 4

6 + 4 = 10 and 9 + 1 = 10, now Multiply 4 x 1 = 4 and put it at the end.

Then subtarct 6 from 1 and you get 5 or 9 from 4 and you will get 5 either subtraction is ok...so final answer is 54

Another e.g.

8 x 7

8 2

7 3
---------
5 6 (2 x 3 =6) and 8-3 or 7-2 = 5.

Easy way to make kids remember their tables.


25 x 25 = 625

whenever you are multiplying same digits....with 5 at the end (25 x 25 or 35 x 35 55 x 55 etc..) Write 25 at the end and multiply the first digit by itself and add same number to the multiplication number. So for 25 x 25, 2 x 2 + 2 = 6 and 25 at the end.

For 55 x 55 (5 x 5 + 5 = 30) and hence 3025 simple emough to do in your head.

multiplication of two digit numbers...slightly tricky but useful if you can remember...

35 x 26 =

3 5

2 6
-----------

multiply 5 x 6 = 30

then [{3x6) + (5x2)} = 28] cross multiplication and add.

and 3 x 2 = 6 (first column)

Now start putting them down.

30, 28 and 6

last digit of the answer is 0. Then add 28 to 3 that gives 31 (carry over). So next digit is 1 and add 3 (carry over) to 6 (of 3 x 2) to make it 9.

So answer is 9 1 0


Good luck.

Answer 2

No, but I would like to.

Answer 3

What?