1. Logic Puzzle - Navajo Math Circles

1. Logic Puzzle: There are two ducks in front of a duck, two ducks behind a

duck and a duck in the middle. How many ducks are there?

Answer: Three. Two ducks are in front of the last duck; the first duck has two

ducks behind; one duck is between the other two.

2. Logic Puzzle: Five people were eating apples, A finished before B, but

behind C. D finished before E, but behind B. What was the finishing order?

Answer: CABDE. Putting the first three in order, A finished in front of B but

behind C, so CAB. Then, we know D finished before B, so CABD. We know E

finished after D, so CABDE.

4. Logic Puzzle: A man has 53 socks in his drawer: 21 identical blue, 15

identical black and 17 identical red. The lights are out and he is completely in

the dark. How many socks must he take out to make 100 percent certain he has

at least one pair of black socks?

Answer: 40 socks. If he takes out 38 socks (adding the two biggest amounts, 21

and 17), although it is very unlikely, it is possible they could all be blue and red.

To make 100 percent certain that he also has a pair of black socks he must take

out a further two socks.

5. Logic Puzzle: The day before two days after the day before tomorrow is

Saturday. What day is it today?

Answer: Friday. The ¡°day before tomorrow¡± is today; ¡°the day before two days

after¡± is really one day after. So if ¡°one day after today is Saturday,¡± then it

must be Friday.

7. Logic Puzzle: You¡¯re at a fork in the road in which one direction leads to the

City of Lies (where everyone always lies) and the other to the City of Truth

(where everyone always tells the truth). There¡¯s a person at the fork who lives in

one of the cities, but you¡¯re not sure which one. What question could you ask

the person to find out which road leads to the City of Truth?

Answer: ¡°Which direction do you live?¡± Someone from the City of Lies will lie

and point to the City of Truth; someone from the City of Truth would tell the

truth and also point to the City of Truth.

10. Logic Puzzle: A farmer wants to cross a river and take with him a wolf, a

goat and a cabbage. He has a boat, but it can only fit himself plus either the

wolf, the goat or the cabbage. If the wolf and the goat are alone on one shore,

the wolf will eat the goat. If the goat and the cabbage are alone on the shore, the

goat will eat the cabbage. How can the farmer bring the wolf, the goat and the

cabbage across the river without anything being eaten?

Answer: First, the farmer takes the goat across. The farmer returns alone and

then takes the wolf across, but returns with the goat. Then the farmer takes the

cabbage across, leaving it with the wolf and returning alone to get the goat.

17. Logic Puzzle: If five cats can catch five mice in five minutes, how long will

it take one cat to catch one mouse?

Answer: Five minutes. Using the information we know, it would take one cat

25 minutes to catch all five mice (5¡Á5=25). Then working backward and

dividing 25 by five, we get five minutes for one cat to catch each mouse.

19. Logic Puzzle: There are three bags, each containing two marbles. Bag A

contains two white marbles, Bag B contains two black marbles, and Bag C

contains one white marble and one black marble. You pick a random bag and

take out one marble, which is white. What is the probability that the remaining

marble from the same bag is also white?

Answer: 2 out of 3. You know you don¡¯t have Bag B. But because Bag A has

two white marbles, you could have picked either marble; if you think of it as

four marbles in total from Bags A and C, three white and one black, you¡¯ll have

a greater chance of picking another white marble.

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download