It normally takes Claudio 60 minutes to complete a daily task, but when he works with Francesca, he works 20% faster than usual. Together, they complete the task in 30 minutes. Assuming that they worked together but independently at constant rates, how long would it take Francesca to complete the task on her own?
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Took me like 3 minutes to even realize his rate changes when he's with her lol. Classic trap.
The wording 'works 20% faster than usual' is so easy to miss.
So Claudio's rate together = 1.2 x (1/60) = 1/50. Then combined = 1/30, so Francesca = 1/30 - 1/50 = 1/75. Answer is 75.
This is the fastest way. Nice.
This is a tough one, definitely upper 700s. The rate change for Claudio is subtle and easy to overlook. Got 80 first because I forgot the 20% boost.
Yeah the 20% boost is the whole test here.
Why does working with someone make him faster though? Makes no sense physically but okay GMAT.
Just GMAT logic, don't overthink it haha.
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.