We reserved this Sutra for the last of our 30 MATH-Inic Specials for Christmas because it depends largely on how much one has mastered the concepts presented in the previous specials. It also encourages adaptation and stimulates creativity because it shows how some problems can be easily solved By Inspection or By Mere Observation.
In his book “Discover Vedic Mathematics”, Sir Ken Williams wrote “ Sometimes the answer to a problem appears as soon as we look at it; sometime we calculate an answer and then realize that it should have been obvious from the start. So It is worth looking carefully to see if a question has some characteristic which makes the answer obvious.”
As an example, we used 6,789 x 9,999. The answer can be readily obtained by using two sutras, By one less than the one before and All from 9 and the last from 10.
The first part of the answer comes from 6789 – 1 = 6788, while the second part is the 10’s complement of 6,789: 10,000 – 6789 = 3211. So, 6,789 x 9999 = 67,883 ,211.
Or after getting the first part 6788, just get the 9’s complement of 6788. In case there is a confusion in what rule to follow, it is best to use use the last by the last”. The last digits of the factors are 9 and 9 so the last digit of the product must be 1.
Just by looking at the figures, we can announce the answer.
An interesting application of this is getting the recurring decimal equivalent of a fraction with a denominator of 13 like 5/13, for instance.
- 5 x 7 = 35 (By Mere Observation)
- 35 x 11 = 385 (By Mere Observation)
- 385 x 999 = 384,615(By Mere Observation)
- 5/13 = 0. 384615…
1/1001 = 0.000999
5/ (7 x 11 x 13) = (5 x 999)/1,000,000)
5/13 = (5 x 7 x 11 x 999)/1,000,000