60(x+6)=80(x-3) gives 20x=600, x=30, and the distance between Party A and Party B is 60 * (30+6) = 2 160km.
Many times, you have to try all the locks instead of putting all the keys in.
The result is that the first key needs to be tried 10 times, the second key will come down 9 times in turn ... and finally 1 time.
That is 1+2+3+4+5+6+7+8+9+1 0 = 55, but the last 1 time doesn't need to be tried because only1key and1lock are locked, 54.
3. Because every two people have one game, everyone has three games, and because the victories of Party A, Party B and Party C are the same, Party A won two games, but Ding didn't win one.
Suppose the distance between two cars is 272 kilometers after x hours.
The equation 48x+56x=272- 12 is obtained, and x=2.5 is obtained by solving the equation.
5. Suppose A has X books, then B has 450-x books, because the books on the two shelves are the same after moving, and the equation can be obtained.
X-25=450-x+25，2x=500，x=250，B = 450-250=200。
6. Because every two people have to play one game, and each person has at most four games, A has already played four games, so A played with everyone.
Because Ding only played 1 game, Ding only played 3 games with A, so B played all the games except Ding.
C played twice, but both A and B played with C, so C didn't play with Xiaohua. Finally, Obana A and B came on stage, so Xiaohua played two games.
My answer is more difficult, I hope everyone will understand. .....
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