My neurons have gone from coach potato to Cross Fit. After working on the questions from my last post, they are shouting “STOP!” Hopefully, they don’t take matters into their own dendrites or I’m in trouble.
What about you? The people have spoken in response to the post on brain teasers from William Poundstone’s book Are You Smart Enough To Work at Google? In a light turnout, the majority voted to warm up their grey matter on grey days and work on the three puzzles posted.
There is more than one way to solve each puzzle. This point succinctly sums up the value of Poundstone’s work. The benefit is in flexing our intellect and creativity to figure out a solution with the ability to explain it. If you’re done with your mental workout and want to know potential answers, keep reading! If you just want an open book test and get the answers, keep reading! The best answers posted from the book are posted first. My answers are listed next. Note the distinction.
Hint: Have pencil and paper handy to diagram the first two solutions. It helps.
1. Using only a 4- minute hourglass and a 7-minute hourglass, measure exactly 9 minutes.
Best answer: Assume both hourglasses start at 0 minutes. Start both hourglasses.
When the 4 minute hourglass runs out, turn it over. (Potential for 8 minutes)
When the 7 minute hourglass runs out, the 4 minute hour glass will have have 1 minute left on its second run. (8-7)
Turn over the 7 minute hour glass for the second time. When the 4 minute hourglass runs out for the second time, there will be 1 minute left in the bottom of the 7 minute hourglass. So far, you’ve measured 8 minutes. ( 7+1)
Turn over the 7 minute hourglass and let the last 1 minute roll back into the top of the hourglass. 7+1+1= equals 9 minutes.
Susan’s answer: Turn over the 7 minute hourglass. As it runs out, start the 4 minute hourglass. When the 4 minute hourglass is half way through ( 2 minutes) stop it by turning it on it’s side. Voila – 9 minutes.
2. There are three men and three lions on one side of the river. You need to carry them all to the other side, using a single boat that can carry only two entities at a time. You can’t let the lions outnumber the men on either bank of the river because they’d eat them. How do you get them across?
Diagram this answer as you read it. It’s the shortest way to “Ah-Ha!”
Best answer: Assume that lions cannot maneuver boats. You need to keep a man onboard to drive the boat.
First trip: One man and one lion cross. The lion stays, the man returns. One lion on one side; two lions and three men on the other still need to cross.
Second trip: One man and one lion cross. Man pushes lion out. Two lions remain, the man returns. Two lions on one side, two men on the other still need to cross.
Third trip: Two men cross. Two men and two lions on one side, one man and one lion on the other still need to cross. Return one man and a lion in the boat. ( You have to bring the lion in the boat on the return trip or you would leave one man and two lions).
Fourth trip: Leave the returned lion. Two men cross. Three men and one lion on one side, two lions remain on the other still need to cross.
Fifth trip: Send a man to get a lion. He’s supposed to “coax” it into the boat. Three men and two lions on one side, one lion still needs to cross.
Sixth trip: Send a man to get the remaining lion. ( I guess the one who knows how to coax a lion into a boat.) All are happily now on the other side.
Susan’s answer: Didn’t get it. If the lion eats the man in the boat on the first trip, the whole thing blows up.
3. A man pushed his car to a hotel and lost his fortune. Share what happened in a single sentence.
Best answer: He was playing Monopoly.
Susan’s answer: Ah-Ha. Caught myself over thinking again.
Now that I’ve subjected you to this mid winter mental workout, I’ll let you in on a secret. I hate brain teasers and puzzles. They push my comfort zone. They make me work when I want to be lazy. They force me to confront many possibilities when one is just fine. Like challenging other muscles in a workout, they make my head hurt.
After scanning Poundstone’s book, I conclude that “Do brainteasers” is the “Eat my spinach” advice of mental agility. They build stronger muscles for reasoning and creativity, whether I like it or not.
Reference: Poundstone, W. (2012). Are You Smart Enough To Work At Google? New York: Little, Brown and Company.