运输商每天收到的订单数量相同。目前，他有一些待处理订单(积压)要发货。如果他使用7辆卡车，则在第4天结束时，他可以清除所有订单。或者，如果他只使用3辆卡车，那么所有订单都将在第10天结束时清算。至少需要多少辆卡车，才能在第5天结束时没有待处理的订单?
(A) 4
(B) 5
(C) 6
(D) 7答案： (C)
解释：
Let each truck can take at most x units. Let the daily order be y and let backlog be z.
7*4*x = 4y + z
3*10*x = 10y + z
We need value of (5y + z)/5 in terms of x.
We can get value of y by subtracting first from second
6y = 2x
y = x/3
We can get value of z by substituting value of y in first equation
4y + z = 28x
4(x/3) + z = 28x
z = (80/3)x
So the value of (5y + z)/5 is 5*(x/3) + (80/3)x which is 17/3
So almost 6 trucks needed.这个问题的测验