satyavegi wrote:Aneesh
Can you explain me the concept of arriving the methodology of working out the problem
regards
Vegi
Hi Vegi,
I will try to articulate my thought-process.
Given: 3/(p+q)=l/(q+r)=m/(r-p)
I can see a lot of unnecessary variables - p, q, r - in the equations above. The question is about 'l' and 'm', which can be written in the form of the unnecessary variables as follows:
l = 3*(q + r)/(p + q)
m = 3*(r - p)/(p + q)
Pause for a few seconds here. Remember this is a problem that is expected to be solved inside two minutes. We've to manipulate the equations above such that p,q and r vanish.
Adding and Subtracting the two equations are two very common approaches.
If you try adding them:
l + m
= 3*(q + 2r - p)/(p + q)
p, q and r don't vanish.
Try subtracting them:
l - m
= 3*(p + q)/(p + q)
= 3
First r vanishes, and them (p + q) vanishes.
Now, look for the option for which l - m is not equal to 3.
Having said all of that, there is no substitute to practice. When you have solved a lot of similar problems, it becomes easier for you anticipate what will work out and what will not.
Does that help?
