Machine problem

[moneyman]

Six machines each working at the same constant rate together can complete a given job in 12 days.How many additional machines , each working at the same constant rate,will be needed to complete the job in 8 days??

2
3
4
5
6

[zacky]

Hello,

I think you have to calculate how percentage of evolution of machines you need comparing to the time reduction ration.

Time reduction ratio : 12 days / 8 days = 1.5
Than 6 machines * 1.5 = 9 machines

Finally you need to add 3 machines.

Am I right ?

Zacky

[jimbow]

Other possibility:

6 machines for 12 days
3 machines for 24 days
1 machines for 72 days

thus
1x9 machines for 72/9=8 days

[wongee]

Another:

Mach Days
6 12
x 8

Inverse proportion = to finish in LESS days we need MORE machines

6 * 12/8 = 9

(9-6) = 3 additional machines