Math w/o calculator :
Now a single digit precision can be achieved by rounding the numbers to nearest digit and then multiplying both.
That's what I learnt in school and had been doing ever since.
Example : How many seconds are in a year?
Ans : 60 * 60 * 24 * 365 = ?
In all cases I don't care about the lower digits. Simply asking if it's some 10 million? or 100 million or billion seconds?
The quick method to find : round all numbers to single digit and multiply.
60 * 60 = 3600 = 4000
4000 * 24 = 4000 * 20 = 80,000
80,000 * 365 = 80,000 * 400 = 30,000,000
Ans : 30 million approximately. Real answer : 30,758,400. Error of 3%.
But this method becomes tricky when both the numbers are near 1 or 2 and the next digit is around 5.
Here's where logarithmic calculation comes in handy.
cont...