In a toy factory, when working together, Mary and Jim can assemble a model car in 12 hours and paint it in 4 hours. If it takes Mary 30 hours to assemble the car by herself, and it takes Jim 12 hours to paint the car by himself, then how many hours will it take if Jim assembles the car and Mary immediately paints it after he is finished?
Answer Choices
Correct answer marked belowSee the full step-by-step explanation
You can see the correct answer above. Sign in for free to unlock the complete worked solution.
Track your performance and improve
Get detailed analytics, unlock full explanations, and move up difficulty tiers as you practice.
Unlock the full explanation
Create a free account to reveal the correct answer, see the step-by-step explanation, and start tracking your GMAT progress.
Thanks! I got confused at first because they give both together and individual times for different tasks. Once I realized it's just combining rates for assembly and then painting, it made sense.
Same here! The wording tripped me up a bit. Did you find it easy after that?
Yeah, it's straightforward once you separate the tasks.
Quick question: for the assembly part, how do you find Jim's rate? I know Mary takes 30 hours and together they take 12, so Jim's rate is 1/12 - 1/30 = 1/20, so 20 hours. Then painting: Mary's rate? Jim takes 12 hours, together 4, so Mary's rate is 1/4 - 1/12 = 1/6, so 6 hours. Total 26. Is that right?
Yes, that's exactly how I did it.
Perfect, thanks!
This was a nice medium difficulty. The key is to not mix up the rates for assembly and painting. I almost used Mary's painting time as her assembly time.
What it tests
Your ability to combine individual work rates, usually by working with the fraction of a job completed per unit of time.
Common trap
Adding the times instead of the rates, or forgetting to take the reciprocal when combining rates.