There are few simple things which make our calculations little faster without efforts. Students applying these simple simple methods in various situation sometimes come across very quick results.
Let us discuss a few
Multiplication by 11
It is the simplest of all next to multiplication by zero.
960403 x 11 = 10564433
How this is done in single line.
Start from right and approach left while adding the current digit to the preceeding digit and at the extremes the two numbers come as they are with carry anywhere if applicable is to be added.
960403 x 11
Step1 ) ________3 last digit as it is
Step 2) _______33 Added 0 to previous digit 3 of original no.
Step 3) ______433 Added 4 to the previous digit 0
Step 4) _____4433 Added 0 to thee previous digit 4
Step 5) ____64433 Added 6 to previous digit 0
Step 6) ___564433 Addded 9 to previous digit 6. this becomes 15. Write 5 and take 1 as carry for next step
Step 7) 10564433 Added the carry 1 to 9. After this there is no more digit to the left so the process completes and the answer is 10564433
Squaring of number ending in 5
To square a number which ends in 5 is very easy. For eg to square a number 25,35,15,85 or any other
The last two digits will always be 25 because both 5 will multiply to give 25.
What will come before 25 ? Take the digits ahead of 5 in the original number and multiply it with one more.
That means for a number say 85
The last digits will be ____25
And before that will come 8 x (8+1) = 8 x 9 =72
So the answer is 725
You can check this with 25 .
Last digit ____25
Before will come 2 x (2+1) = 2 x 3 =6
So the answer is 625
This will work with bigger numbers also
For eg 115
Last digit ______25
Before will come 11 x (11+1) = 11 x 12 = 132
So the answer is 13225