Ten bags each contain nine pieces of gold. The gold pieces are all supposed to weigh 1 ounce, but the pieces in one bag weigh only .9 ounces. Use an accurate scale just once to find which bag contains the lighter pieces.
A:
Take 1 piece from the 1st bag, 2 pieces from the 2nd bag, and so on up to 9 pieces from the 9th bag. The total weight W would normally be 45. If it is, the 10th bag has the lighter pieces. Otherwise the number of the guilty bag is (45 - W) x 10 .
Q:
There are 3 incandescent light bulbs in one room and 3 switches for these bulbs in another room. No light from the bulbs can be seen outside of their room. You are allowed to enter the room with the bulbs only once. How can you figure out which switches are connected to which bulbs?
A:
Start with all switches off. Turn switch A on and wait 10 minutes or so. Turn A off and B on. Go into the room. Light A is off and warm, B is on, and C is off and cold.
Q:
You have 2 lengths of fuse and 2 matches. One fuse will burn from start to end in 10 minutes, and the other in 15 minutes. However, their burn rate is not steady along their lengths. Measure 20 minutes of time.
A:
Light both ends of the 10 minute fuse at once. When those burning ends meet, light the 15 minute fuse. When that is finished burning, 20 minutes are up.
Q:
You have 3 cultures of highly contagious and deadly germs. As part of an important experiment you must squeeze each culture once with your entire hand. However, you have only 1 pair of latex gloves. You must not contaminate any culture with another or with germs from your skin. The gloves can be worn on either the left or right hand. How can you complete your experiment without contaminating anything?
A:
Put both gloves on the same hand and squeeze the 1st culture. Take the outer glove off and turn it inside out (its now dirty inside and clean outside). Use the glove that is still on to squeeze the 2nd culture. Put the second glove back on over the first (so their dirty sides touch) and squeeze the 3rd culture.
