Brainteasers asked in Interviews

[klorpet]

Sometimes interviewers like to put you on the spot and ask puzzles or brainteasers. The value in these is hard to determine but some feel that it allows them to get a feel for how your mind works (analytically) and how well you face pressure and time constraints.

Here's one for you to try:

You are given two pieces of string that will burn for a total of 3 minutes each. However the burn rate is uneven throughout both strings, so that they will burn quickly at first then slow down then speed back up, but always burns for a total of 3 minutes.

Using just these two pieces of string and a box of matches how can you measure 4 and a half minutes?

[Rahulbatra]

Cut one of the strings into half. Burn the first string that was uncut which will have 3 miutes to completely burn. Than when the before the first string is totally burned, attached the half string to the end of the burning string so it will add 1 and a half more minutes.

[klorpet]

No I'm afraid you haven't got this one yet. The string burns at uneven rates so you could cut the string in half and one half might burn fo 2 minutes and 10 seconds and the other half for 50 seconds.

[santi]

i have another solution instead of cutting strings into half,i would prefer to fold one of the strings in middle and combine all the three ends together and light it with match.
The string which was folded will burn exactly 1.5mins irrelevant to the slow or fast burning.
totally we will get 3+1.5=4.5 mins

is it correct ????

[ksaxena]

Correct answer is follows:
lit 1st thread at one end, it finish 3min gone. Now after that lit 2nd thread from both the side. 1.5 min

Note: litting from both side will give you 1.5 min