I am posting some methods which I think might help you(especially those who face some kind of time crunch during maths part)
Before I write the methods, I would like to let you know something about myself, I am still in my pre-final year of undergraduate degree(Engineering) and I am very careless student because I never go to my Engineering classes with a calculator, but due to this irregular habit I have developed a great art of doing calculations very fast without calculator.
So here are some of the methods which will be extremely beneficial for Questions like this :
https://www.beatthegmat.com/ps-t33638.html
I would like to take the above question as an example:
9/25 + 15/32 +c =1
We have to add 9/25 and 15/32
So what we do : 9/25 + 15/32
9*32 + 15*25/LCM
Here LCM is 25*32
Now how I calculate this 25*32
25 * 30 + 25*2
25*30 ==> we orally know 25*3 is 75 and if a number is multplied by 10 we add 0 behind that number:
So 25*30 ==750
and 25*2 = 50
So whats 25*32??
Now can you verbally calculate 25*32!!
Take the numerator part:
9*32 + 15*25
what we do again, we again make 9*32 to a multiple which can be orally calculated
that is, in this case its 10
so we do 10*32 -32
ie : 320-32
still this subtractions can be simplified by again turning to nearest 0
eg 320 -30 = 290 and now subtracts 2 further
= 288
It looks big while writing just for explanation(you don't need to give any explanations in exam so you can go pass through this kind of calculations within seconds!!)
Now take 15*25
here 15*20(Again putting back to nearest 10th multiple number)
15*20 + 15*5 [even if you don't remember any multiple of 5 eg: 17*5 or 19* 5 etc etc......just multiply and divide 5 by 2)
300 + 15*(10/2) [ 150/2]
300 + 75 == 375
So look how quickly you can reach
9/25 + 15/32 = (375 +288)/800
= 663/800
Now c =1- 663/800
c = 137/800
And if we are asked to compare the fractions, we can do that by making the dinominators of all the fractions equal as I have done in this question:
https://www.beatthegmat.com/ps-t33638.htm
You can apply this method of converting the digit you want to multiply to nearest 10th Multiple in any kind of calculations and see how quickly you will be able to solve the calculation part.
I learned lots of stuffs from this FORUM and in fact I am still in a learning process, but I felt its imperative to give back something and this is the best possible way I can contribute
Karan
