A man covers certain distance by his car, had he moved 6km/hr faster he would have taken 4 hours less, if he had moved 4km/hr slower he would have taken 4 hours more.Find the distance.
Please help with the approach
If there are options, I will use options. Failing that, I suspect trial and error will be quicker than solving equations. Still if you want equations:
s * t = (s + 6)*(t-4) = (s – 4)(t + 4)
Trial and error gave me 24 speed and 20 time (in around a minute), giving distance of 24 * 20 = 480.
regards
J
what should be the thinking process in trial and error?? is it directly plugging values but it will take a lot of time{certainly more than solving equations}
Varies from question to question, and from person to person. For me, if I have t check less than 10 cases I will definitely do it (not necessarily in first round), more than 30 I will definitely not do trial and error unless I can find some mathematical way of reducing the cases, between 10 and 30 I will decide depending on how complicated the calculations are per case. Your mileage may vary 🙂
regards
J
In the first question the answer comes out to be 12. This is the harmonic mean of 15 and 10. I don’t think this is just a coincidence. Could you please explain.
It isn’t a coincidence – it is because the times are in AM in this particular case. But it will not work for any random times…only if times are in AM will speeds be in HM and vice versa…
On this blog, we just have a few posts of vocabulary and so on; the focus was more on Quant. But you might try T’s blog at http://www.imschennai.in/blog/ , I am sure you will find plenty of useful stuff there!
CAT-holics 
A man covers certain distance by his car, had he moved 6km/hr faster he would have taken 4 hours less, if he had moved 4km/hr slower he would have taken 4 hours more.Find the distance.
Please help with the approach
If there are options, I will use options. Failing that, I suspect trial and error will be quicker than solving equations. Still if you want equations:
s * t = (s + 6)*(t-4) = (s – 4)(t + 4)
Trial and error gave me 24 speed and 20 time (in around a minute), giving distance of 24 * 20 = 480.
regards
J
what should be the thinking process in trial and error?? is it directly plugging values but it will take a lot of time{certainly more than solving equations}
Varies from question to question, and from person to person. For me, if I have t check less than 10 cases I will definitely do it (not necessarily in first round), more than 30 I will definitely not do trial and error unless I can find some mathematical way of reducing the cases, between 10 and 30 I will decide depending on how complicated the calculations are per case. Your mileage may vary 🙂
regards
J
In the first question the answer comes out to be 12. This is the harmonic mean of 15 and 10. I don’t think this is just a coincidence. Could you please explain.
It isn’t a coincidence – it is because the times are in AM in this particular case. But it will not work for any random times…only if times are in AM will speeds be in HM and vice versa…
regards
J
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Hello Sir,
This might be inappropriate ,but i would like to know if you have any such blog for Verbal.
Thanks,
Shivam
On this blog, we just have a few posts of vocabulary and so on; the focus was more on Quant. But you might try T’s blog at http://www.imschennai.in/blog/ , I am sure you will find plenty of useful stuff there!
regards
J
Hi J,
In Q3, what gave away that difference of squares mean [a-b]^2 and not a^2 – b^2.
I tried a lot to figure out the difference, but couldn’t.
Regards,
Shraa
Oh sorry that is a typo it is a^2 – b^2 (which is why it becomes (a+b)(a-b) in the next step).
regards
J
Oh, okay. Thanks a lot, J. 😀
Regards,
Shraa