问题
单项选择题
一件工作甲做6小时、乙做12小时可完成，甲做了8小时、乙做6小时也可以完成，如果甲做了3小时后由乙接着做，那么还需要多少时间才能完成。( )
A．20
B．21
C．22
D．23
答案
参考答案：B
解析：
由题意可得设甲单独完成这项工作需要t1小时，乙单独完成这项工作需要t2小时，所以可以列出方程组成立。解得，t1=10，t2=30，再由题中甲先做3小时后乙做，还需要小时即21小时。正确答案B。
搜题请搜索小程序“爱下问搜题”
corner. Once again, he stopped to look at the shop 小题2:. He felt happy to see the shoes that he wanted very much were still there. He really wanted to have 小题3: for his birthday. Looking down at his old shoes, he felt sorry for himself.