1. On the racecourse, there are three horses, A, B and C. A can run two laps in one minute, B can run three laps and C can run four laps. Now put three horses side by side on the starting line and prepare to start from the same horse. Excuse me: after a few minutes, can these three horses run side by side at the starting line again?

Answer 1 min. Because three horses can run side by side at the starting line, B runs at least 1 lap more than A. After 1 minute, B just runs 1 lap more than A and is at the starting line. So 1 minute is no problem.

2. Two different coins are tangent. When the other circle rolls back to the starting point around the other circle, how many times does the circle * * * rotate?

Answer twice. Draw a picture and arrange it left and right. The coin on the right is stationary. Turn the coin on the left to turn it to the right. I found that the leftmost point at the beginning turned to the left of the right coin. At this time, the coin turns 1 time, so it has to be turned twice.

There are two piles of rice cakes on the table, each pile is three pieces. The pile on the left is 1kg, 2kg, 5kg, * * weighs 8kg, and the pile on the right is 3kg, 4kg, 5kg, * * * weighs 12kg. If the weight of rice cakes on both sides is equal, there are still three pieces on each side.

Answer 65438+ 0kg on the left and 3kg on the right. Or 2kg and 4kg.

Several friends shook hands after the party, and everyone present shook hands with the rest of the participants once, shaking hands 28 times. How many people should there be at least at the party? Please consider yourself a second-grade teacher. How will you solve this problem for your students?

Everyone should shake hands with others, that is, one person should shake hands less than the number of people present 1 time.

Suppose the number of people present is x, think again, if A and B shake hands, B and A don't have to shake hands.

So x(x- 1)/2=56.

X=8(-7 rounding)

There was a theft in the street. The thief was so cunning that he didn't leave any clues at the scene, but the money in the safe was gone. How did the thief know the password? Conan found a small piece of paper at the scene with four numbers written on it: 1008, 1260, 1386, 1 134. But the password can only be three digits. What does it have to do with these four numbers? Suddenly Conan had a flash of light. He did a quick calculation, then pressed three numbers on the safe, and the safe was opened. Do you know the password? How did you get it?

The answer is1+8 =1+2+6 =1+0+3+4 = 91+3+8+6 =18.

The password is 9 18.