Vedic Maths trick
As always, VEDIC MATHS TRICKS are always the best. This VEDIC MATHS TRICK will let you do calculations within a few seconds.
This is the trick exclusively applicable to the multiplications of TWO numbers, whose digits at units place add up to 10 as well as whose digit at tenth's place is same. ( Both these conditions must be satisfied.)
For an example, let's take two numbers 83 and 87 ( note that both the above conditions are satisfied, that is, digit at tenth's place is same and at the units place add upto 10 )
Now, follow the steps.........
1) Firstly, find the product of digits at unit's place, that is, 3*7 = 21
2) Secondly, multiply tenth's place digit by its consecutive number, that is, 8*9 = 72
3) Now finally, your answer is the result in second step followed by the result in first step.
4) Hence, the answer is 7221.
Now, you could do such multiplications orally within few seconds.
it is not hard to think why it works.
let the number be 10a +b and 10a + 10 - b.
10a + 10 - b = 10(a+1) - b.
we want (10a+b)(10(a+1) - b)
= 100a(a+1) - 10ab - b^2 + 10b(a+1)
= 100a(a+1) - 10ab - b^2 + 10b + 10ab
= 100a(a+1) + 10b - b^2.
= 100a(a+1) + b(10-b).
100 * the first digit*(1+first digit) + the product of the two integers which add upto 10.