7. One of Wang Chun, Chen Gang and Yin Hua did something bad. When Miss Li learned of this situation, the three of them said the following words respectively:
Chen: It wasn't me. Yin Hua didn't do it either.
Wang: I didn't do it. Chen Gang didn't do either.
Yin: I didn't do it. I don't know who did it.
When Miss Li asked, she realized that they all told a truth and a lie, and it was Chen Gang who did the bad thing.
8. two cars, a and b, start from a and b respectively, and the directions are opposite. At the time of departure, the speed ratio of Party A and Party B is 5: 4. After meeting,
The speed of A is reduced by 20%, and the speed of B is increased by 20%, so when A arrives at B, B is still 10 km away from A ... Then A and B are 900 km away.
9. Xiao Li and Xiao Zhang start to make the same kind of parts at the same time. Each person can make 1 part per minute, but Xiao Li has to make three parts.
Rest 1 minute, Xiao Zhang will rest every four parts 1.5 minutes. Now they have to complete the task of 300 parts together, which takes 183 minutes.
10, three people, A, B and C, go to buy books, the number of books bought by B is 3, and the number of books bought by C is 1, so three people will buy at least four books altogether.