A problem in lateral thinking...and some more lateral thinking about problems

August 11, 2007

A friend of ours in Hyderabad posed this problem in lateral thinking:

We all know about old fashioned detonator cords – a piece of string attached to an explosive and which burns for a specified amount of time to set off explosion.

Well I have these two pieces of cords of identical length and looks. One burns over half an hour and the other over one hour. I don’t know which the one-hour piece is. To make the matters worse the rate of burning is not uniform along the length in both cases i.e. for all I know one tenth of the one hour cord may burn in 50 minutes and the balance nine tenth in 50 minutes.

All I want is to measure a time of 45 minutes using these two cords and a matchbox full of sticks. How ?

PJs about looking at a watch/ clock / asking the neighbor/ say “tick tick one” and so on - not allowed.

Two separate solutions were thought of and emailed, and for a variation of the second solution,the problem also was modified to say, “a matcbox with just one match”. If you haven’t seen this problem before, think about it. You can email me for both solutions.

But to get to where I am with this problem…as usual, while trying to solve it, I fell to musing….

And of course, a little more lateral thinking tells me that I will follow the directions of the solution, but then go off because the milk is boiling over in the kitchen, and when I come back, the cords would have burnt out…and more than an hour would have gone past!

That reminds me of Swami in R K Narayan’s “Swami and Friends” , whose father sets him a sum about Rama having so many mangoes and Krishna( maybe I have the names in the reverse order) buying so many…at the end of some musing, Swami asks his dad, “were the mangoes ripe?” To him this is crucial to the question..if the mangoes are ripe, the price that Rama will ask will change! He also thinks about whether Rama is a good guy or a scoundrel, which will affect the price that Krishna has to pay!

It also reminded me of those three people I used to detest in school…A, B, and C. These three men (never, never were they women) were a restless set, always painting walls, tilling fields, and for some unknown reason, turning taps on. C was sometimes the evil one of the lot; he would come and empty the tanks which A and B had filled. And they seemed to work from dawn to dusk and never take a tea break or go to the toilet (except of course to fill up those tanks.) I used to think about C being a furtive skunk-type of fellow, sneaking up in the dark to undo A and B’s good work. I used to feel that just engaging a guard (D) at night was a good idea, to safeguard A and B’s work. Also, it would make the sum much simpler for me.

Add the fact that we were still in transition from yards(and chains, yes, that was a unit of length, too,22 chains made a mile) and feet and inches…and you many understand how I hated these fellows.