Work/rate

[billyr]

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

a)2
b)3
c)5
d)6
e)8





Answer b, but how you set up the equation? thanks

[sureshbala]

6 machines take 12 hours. So the work requires 72 machine-hours. To finish the same work in 8 hrs we need 72/8 = 9 machines. Hence 3 more machines are needed

[billyr]

6 machines take 12 hours. So the work requires 72 machine-hours. To finish the same work in 8 hrs we need 72/8 = 9 machines. Hence 3 more machines are needed

Thanks