Psych Intelligence - Problem Solving Activity

Front

Four people come to a river at night. There is a narrow bridge that can only hold two people. They have one flashlight and it must be used when crossing the bridge because it is so dark. Person A can cross the bridge in 1 minute, B in 2 minutes, C in 5 minutes, and D in 8 minutes. When two people cross together, they must go at the rate of the slower person. Can they all get across the bridge in 15 minutes or less? 

Back

Answer: A & B cross in 2 minutes; A returns in 1 min. C & D cross in 8 minutes; B returns in 2. A & B cross in 2 minutes. 

Front

An old money-lender offered to cancel a merchant’s debt and keep him from going to prison if the merchant would give the money-lender his lovely daughter. Horrified yet desperate, the merchant and his daughter agreed to let Providence decide.

The money-lender said he would put a black pebble and a white pebble in a bag and the girl would draw one. The white pebble would cancel the debt and leave her free. The black one would make her the money-lenders, although the debt would be canceled. If she refused to pick, her father would go to prison. 

From the pebble-strewn path they were standing on, the money-lender picked two pebbles and quickly put them in the bag, but the girl saw that he had picked up two black ones. What would you have done if you were the girl?

Back

Answer: When the girl put her hand into the bag to draw out the fateful pebble, she fumbled and dropped it, where it was immediately lost among the others. “Oh”, she said, “well, you can tell which one I picked by looking at the one that’s left.” The girl’s lateral thinking saved her father and herself. 

Front

A man and his two sons want to get across a river. The boat they have available can hold a maximum of only 200 pounds. The father weighs 200 pounds and the sons weigh 100 pounds each. How can all three people cross the river?

Back

Answer: 1st - both sons cross the river, 1 returns. 2nd - Father crosses and son returns. 3rd - Both sons cross. 

Front

Let's suppose you have a dark closet with five hats in it. There are three blue, and two red ones. 

Three men go into the closet and each selects a hat at random in the dark and places it on their head. Once outside the closet, each man is unable to tell what color their own hat is. 

The first man looks at the others and says "I cannot tell what color my hat is!". The second hears this, looks at the other two, and declares "I cannot tell what color my hat is either!".

The third man, who is blind, confidently declares "I know exactly what color mine is!".

Back

Answer: We will call the people A, B & C in the order that they speak.

A does not know what color hat he is wearing. A would only know what color hat he was wearing if he could see that B & C were both wearing red hats, (as there were only two red hats in the cupboard.) This is not the case so either:-

B & C are both wearing blue hats

OR

one of B & C is wearing red and the other is wearing blue

When B speaks we obviously assume he has thought of all of this. When B looks at C if C were wearing red then he (B) would know that he (B) must be wearing blue as they can't both be wearing red. But this does not happen so C must be wearing blue, causing B not to know if he is wearing red or blue:

The third person (C) must be wearing a BLUE hat.