蘇寫求解示?

chasechase12

1. six machine, each working at the same contant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same contant rate will be need to complete the job in 8 days?

ans: 3

2.A company has two types of machine, type R and type S , operating at a contant rate, a machine of type R does a certain job in 36 hours and a machine of type of S does  the same job in 18 hours. if the company used the same number of each type of machine to do the job in 2 hours. how many machines of type R were used?

ans: 6

甜甜圈1234

设rate=x
6*1/x=1/12
得出x=1/72

8天的话，设有n台机器。n*x=n*1/72=1/8
n=9

additional machines=n-原来的6台=9-6=3