How to approach Quantitative Aptitude section

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I would like to share some tips for Quantitative Aptitude section. The questions asked in CGL are very basic and anyone can solve them, but the difference lies in the fact that how much time you are taking in each one of them. Try to solve the questions just by looking at the options(without writing a single word). For e.g. let's take the questions that appeared in CGL 2015 tier-2 - 

Now this an easy question and everyone can solve it by making linear equations or any other method. But first see if this question really deserves your rough space. Since the monthly incomes of A and B are 8x and 5x, their difference will be 3x (or a multiple of 3). Rs. 42,000 is the only option possible because it is the only multiple of 3.

Next question -

Among the given options, 24 is the only number in which the units place digit is twice the tens place digit. No need to form equations.

Next-

HCF of the numbers is 21, hence both the numbers are divisible by 21. By looking at the options we find that 84 is the only number that satisfies this condition.

At least 15 questions can be solved by this method, and the time saved here can be utilized in solving other complex questions...