vanessa can do a job in 12 days. after she has worked for 4 days, she is joined by susan, and they finish the job together in 2 more days. how long would it have taken susan to do the whole job herself
well, vanessa worked for four days, so she did 4/12 of the job (1/3).
So in the two-thirds left
time=jobleft/rate
where jobleft is 2/3 job and
rate=vanessarate + susan rate or
jobleft/2days=job/12days + susanrate
or 2/3 job/ 2= job/12 + susan rate or
susan rate= 2/6-1/12= 3/12=
susan rate= 1job/4days