Question 888482
Set C = Carol's rate in projects per hour
    M = Mary's rate is projects per hour
4*( combined rates for Carol and Mary ) = 1 project completion
 4(C+M) = 1
Since Carol's rate is 2 times Mary's rate we can rewrite the above
 {{{4(2M + M) = 1}}} where C = 2M
 {{{8M + 4M = 1}}}
 {{{12M = 1}}}
divide each side by 12
 M = 1/12
Mary's rate is 1/12 project per hour
She can complete 1/12 of the project in one hour.