Can you solve it in 30 seconds??

This was a question asked in a Personal Interview of Microsoft corporation..

You have two ropes exactly of same length.These two burn with a uniform constant rate(not necessary that you burn them simultaneously) and are burned up completely in 30 minutes.Also you have been provided with matchsticks.Using these materials how will you measure 45 minutes???

Details You can't fold the rope and you do NOT have a measuring instrument. Inaccuracy may be allowed if its not too large(because you have to imagine it practically). There is sufficient number of matchsticks

#Algebra

Easy Math Editor

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Comments

Put both the ropes parallel and the ignite both ropes but from opposite sides.A point will come when the fire will cross each other.put out one of the rope and let burn the other completely so that it will tell you 30 min and join the incompletely burned rope to the end of this rope which will give you additional 15 min because when ignited simultaneously in opp direction the point of crossing will be at 15 min.

Aakash Deshpande - 7 years ago

This works because it is given that it burns in a uniform constant rate. But suppose the case is that it doesn't. It may so happen that the first 1/3 of the rope will burn in 25 min and rest 2/3 will take just 5 min, or anything. Then, this wouldn't work.

Shashwat Gupta - 6 years, 12 months ago

burn one from both sides and after it has burns, burn the other one. 15+30=45

Daksh Walia - 7 years ago

Burn one from the end and then the other from the middle. (30+15)

Shashwat Gupta - 7 years ago

Burn 1st rope n when it burns half than start to burnother rope

Ananya Mittal - 7 years ago

How will you know exectly that is burned half???

Aakash Deshpande - 7 years ago

Ya,it was mentioned that there is no "measuring" instrument.

Varenya Srivastava - 7 years ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$