Brain Teaser of the Week

Brain Teaser #3

A ribbon is 30 inches long. If you cut it with a pair of scissors into one-inch pieces, how many snips would it take?

{Solution}

Twenty-nine snips. The last two inches are divided by one snip.

Brain Teaser #2

Katie the cook was in a predicament over a pie. The recipe called
for baking it for exactly nine continuous minutes, but all she had in
the way of clocks were two egg-timers. The first one measured a
period of four minutes, and the second one seven minutes. If there
are no graduations on the egg-timers, and sand cannot be removed or
transferred from them, what is the quickest way that Katie can
measure nine minutes with the two timers?

{SOLUTION}

Put the pie in the oven and start both egg-timers. When the first one
runs out, turn it over. (Elapsed time so far is 4 minutes.) When the
second timer runs out, turn it over, too. When the first one runs out
again (after a total of 8 minutes), the second timer has been running
for one minute since it was restarted, so turn it over again.
When the one minute runs out, the pie is ready.

Brain Teaser #1

A Ferrari is traveling at 30 miles per hour on a head-on collision course with a Maserati, which is being driven at a leisurely 20 miles per hour. When the two cars are exactly 50 miles apart, a very fast fly leaves the front fender of the Ferrari and travels towards the Maserati at 100 miles per hour. When it reaches the Maserati, it instantly reverses direction and flies back to the Ferrari and continues winging back and forth between the rapidly approaching cars. At the moment the two cars collide, what is the total distance the fly has covered?

{Solution}

At first glance it may seem that a horrendous calculation is necessary to solve this: the sum of an infinite series of numbers that get smaller and smaller as the cars approach each other. But if you focus on time rather than distance, a solution is easy. The cars are 50 miles apart and traveling towards each other at a combined speed of 50 miles per hour, so they will meet in one hour. In that hour, a fly that flies at 100 miles per hour will naturally travel 100 miles.