Last weekend we had a birthday for our classmate Zhang Xiaohui. She is younger than me, but I am shorter than her. And she looks stronger. Of course she is heavier than me. We went to a shop to buy a present for Xiaohui. What did we buy? We bought a doll for her. Because she told me " I haven't got a lovely doll." When she got our present she looked excited. She was very happy. We went to the zoo. We saw elephants. We wanted to row a boat in Jingming park, but it was later, we had to went home. We had a good time on that day.

①一根绳子，第一次剪去全长的 $\frac{3}{5}$ ，第二次剪去剩下的 $\frac{1}{3}$ ，一共剪去全长的几分之几？

②六（1）班同学为云南鲁甸灾区孩子献爱心，第一组捐款380元，第二组捐的是第一组钱数的 $\frac{3}{4}$ ，是第三组捐钱数的 $\frac{1}{2}$ ，第三组同学捐款多少元？

③自从改进了生产技术后，工厂第一个月节约用煤 $\frac{2}{5}$ 吨， 第一个月比第二个月多节约了 $\frac{1}{3}$ ，两个月一共节约了多少吨煤？

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打开收音机的开关，将旋钮调到没有电台的位置，并将音量开大．取一节干电池和一根导线，靠近收音机将导线的一端与电池的一极相连，再用导线的另一端与电池的另一极时断时续的接触，会听到收音机发出“咔咔”声，这一现象说明周围的空间存在（　　）