Working alone Joan finish the job in 60 minutes, which means every minute she does 1/60 of the whole job. suppose the sister can finish the job alone in x minutes, every minute she does 1/x of the whole job. together they do (1/60 +1/x) part of the job every minute. for 40 minutes they finish the whole job: (1/60 +1/x)*40=1 (1 represents the whole job) 40/60 +40/x =60/60 40/x=20/60 x=120 so it will take the sister 2 hours to finish the job alone
You will need to raise the unit selling price... do you need know by how how much? well it it will have to be a 25% increase for the unit selling price to maintain the groos margin percentage
