Ideas for adding and subtracting well
Addition is perhaps the most critical skill when it comes to developing your calculations. As you would see through the discussions in the remaining chapters of this section of the book, if you have the ability to add well you would be able to handle all the other kinds of calculations with consummate ease.
Skill 1 for addition: The ability to react with the addition of two numbers when you see them. The first and foremost skill in the development of your addition abilities is the ability to react to 2 two digit numbers when you come across them. You simply have to develop the ability to react with their totals whenever you come across 2 two digit numbers.
For instance, suppose I were to give you two numbers at random― 5, 7 and ask you to STOP!! STOP YOUR MIND BEFORE IT GIVES YOU THE SUM OF THESE TWO NUMBERS!! What happened? Were you able to stop your mind from saying 12? No! of course not you would say.
TRY AGAIN: 12 + 7 STOP YOUR MIND!! You could not do it again!!
TRY AGAIN: 15 + 12 STOP!! Could not?
TRY AGAIN: 88 + 73 = ?? STOP!!
If you belong to the normal category of what I call gaddition disabled aspirantsh you did not even start, did you?
TRY AGAIN: 57 + 95 =??
TRY AGAIN: 78 + 88 =??
What went wrong? You are not used to such big numbers, you would say. Well, if you are serious about your ability to crack aptitude exams, you better make this start to happen in your mind. You would know what I mean if you just try to look at a 5 year old child who has just learnt to add, struggle with a calculation like 12 + 7 on his fingers or his abacus.
His struggle with something like 12 + 7 or even 15 + 12 would be akin to the average aspirantfs ability to react to 88 + 78. However, just as you know 15 + 12 is not a special skill so also 88 + 78 is not a special skill. It is just a function of how much you practice your calculations especially in the domain of 2 digit additions.
So what am I trying to tell you here?
All I am trying to communicate to you is to tell you to work on developing your ability to react to 2 two digit numbers with their addition as soon as these numbers hit your mind. What I am trying to tell you that the moment you make your mind adept at saying something like 74 + 87 = 161 just the way you would do 9 + 6 = 15 you would have made a significant movement in your mindfs ability to crack aptitude exams. Why do I say that\ you might be justified in asking me at this point of time? In order to answer your question I would like to present the following argument to you:
In numerical questions, a normal student/ aspirant would be roughly calculating for approximately 50% of the time that he/ she takes to solve a question. This means that half the total time that you would spend in solving questions of basic numeracy or data interpretation would essentially go into calculations. Thus, if the test paper consists of say 30-40% questions on basic numeracy and data interpretation you would be expected to spend somewhere between 36 to 48 minutes on these questions\ which would in turn translate to approximately 18 to 24 minutes in calculations inside the test paper.
So the contention is this: If you can improve your calculation speed to 5x, the time you would require to do the same calculations would come down to 1/ 5th of your original time. In other words, 18 minutes would come down to 3.6 minutes\ a saving of 14.4 minutes; 24 minutes would come down to 4.8 minutes\ a saving of 19.2 minutes just by improving your calculation speed!!
In an exam like the CAT where you would always run out of time (rather than running out of solvable questions) 19 extra minutes could easily mean anywhere between 15– 20 marks (even if you able to solve an additional 6– 7 questions in this time). So those candidates waiting for CAT result should know that 15– 20 extra marks in the prelims exam could very well make the difference between getting a chance to write the mains examination in the same year versus going back to the drawing board and preparing for the prelims for another year!!