tough questions

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tough questions

Post by paridhi on Fri Jul 21, 2017 8:34 pm

Did anyone solve 18-19?

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Re: tough questions

Post by Human on Fri Jul 21, 2017 8:46 pm

Was it the rope one?

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Re: tough questions

Post by Human on Fri Jul 21, 2017 8:50 pm

I wrote 18 as d (29)

And 19 as b

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Re: tough questions

Post by paridhi on Fri Jul 21, 2017 9:10 pm

How did you solve

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Re: tough questions

Post by Human on Fri Jul 21, 2017 9:14 pm

I didn't solve 19th.
For 18th
I tried to turn the ropes to make maximum intersection

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Re: tough questions

Post by shubham on Fri Jul 21, 2017 9:57 pm

For the 18th one, I can give you a start but can't explain the whole solution here. The minimum time you can count is 3.25 minutes.
To get the minimum time (least count) 3.25 mins, do this:

Take one rope and light it from both ends. At the same time take the other three ropes and light just one end of each.
When the 1st rope burns completely, it means half an hour is over.
Then light the other end of one rope which has been burning since half an hour.
When this rope burns completely, it means another 15 minutes have passed.
Then light the other end of one rope which has been burning since 45 minutes(half an hour + 15 mins).
When this rope burns completely, it means another 7.5 minutes have passed.
Then light the last rope from the other end which has been burning since 52.5 mins.
This rope will burn completely in another 3.25 mins.

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Re: tough questions

Post by shubham on Fri Jul 21, 2017 10:02 pm

I got 26 as answer.

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Re: tough questions

Post by paridhi on Fri Jul 21, 2017 11:07 pm

@shubham but in question it was mentioned we can light rope only at either of the end

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Re: tough questions

Post by shubham on Sat Jul 22, 2017 5:18 pm

Yeah that does not mean that you can light only one end of each rope. The English comprehension might be debatable, but there are evidences and indications in the question which tell us that we can light both ends of the rope.
"For example, the time taken to burn one rope if burnt from only one end is 1 hour"..........this statement gives a hint that we can choose to light both ends of the rope.

The statement just means that you can light the rope only at the ends and not somewhere in the middle.

Also if the statement would mean that you can light the rope only at one end, then the answer would be very small, way below 20.

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Re: tough questions

Post by Human on Sat Jul 22, 2017 5:53 pm

It might be less than 20 if rods were used instead of ropes.

We can turn the ropes!!

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Re: tough questions

Post by shubham on Sat Jul 22, 2017 9:50 pm

What do you mean by turn the ropes??

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Re: tough questions

Post by Sai1704 on Sat Jul 22, 2017 11:26 pm

He probably means fold but it shouldnt matter because lighting it anywhere other than the end is meaningless, because one segment will almost surely burn faster than the other. So lighting it at one/both ends is the only way to go

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Re: tough questions

Post by shubham on Sun Jul 23, 2017 8:29 am

Yeah right !!

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Re: tough questions

Post by Human on Sun Jul 23, 2017 3:28 pm

No.
I meant overlapping 2 or more ropes by turning them

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Re: tough questions

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