HOW TO USE APPROXIMATION TECHNIQUE :
There are many questions in quantitative, DI and DS section where one don't have to actually solve the whole question. One can find the right solution by approximation. To reach to teh right solution by approximation, first have a look at the options given to you and then decide the method to be adopted for approximation. If the range of the option given is very wide then you may round off the digits to carry out calculations.
You may also guess the answers by using following rules:
1) If you multiply any two odd number the result is always odd.
2) If you multiply any number of number and if any of them is even the final result is even.
3) Rules for identifying if a number is multiple of 3, 4, 5, 6, 7, 8, 9, 10, 11 etc.
4) Other common rules of number system.
We give you an example here :
Q1. Find the value of 3.36* 4.43
Options : a) 15.1108 b) 11.7708 c) 14.8848 d) 20.8848
You don't have to actually multiply the digits to get the answer. You can straight away eliminate option b and d as the product of any two number having value 3.XY and 4.PQ will always be more than 12 and less than 20.
Now you see the number 3.36. The number 336 is divisible by 3. So any number multiplied by 336 will be divisible by 3.
Now Check 15.1108 . 1+5+1+1+8 = 16 which is not divisible by 3 so the correct choice is c.
Similarly there are so many ways to guess the answer or estimate an answer that I can write a whole book on it. Try to develop these skills.