Free GRE Prep Hour: Work Problems

[@Kings_707]

Thank you very much

[@manhattanprepgre7390]

You're so very welcome!

[@AbrahamKidan1]

that is great !!

[@joeboxter3635]

You made mistake, I believe. At @23:00, you say Betty and Cathy can do it twice as fast (i.e., 1/2 the time), that does not mean that the sum of Br + Cr = 1/2. It's actually the case that Br + Cr = 1/2 (Ar + Br). Then you need to figure out from this Cr, by herself. And Ar + Br = 1/4 + 1/3. Six is not the right answer. So, it would be 2(1/4 + 1/3) = (1/3 + Cr). Then once you have Cr, you would get the time from Ct = 1/Cr Having said that, you are a good presenter of this material and very knowledgeable. I especially appreciate your video on ratios.

[@manhattanprepgre7390]

Hi @joeboxter3635 - great question! The 1/2 on the right side of the equation isn't "1/2" in the sense that it is "half his time" but it represents doing 1 doghouse in 2 hours (1 over 2) because that is twice as fast as Alejandro's 4 hours. Also note that in your equation, you are taking 1/2 of the rate Alejandro and Betty working together, which is NOT what the question says in terms of the relationship (B and C together are double the rate of Alejandro. If you wanted to write that as an equation, it would be Br + Cr = 2(Ar), which would then give you the equation I provide in the solution: 1/3 + Cr = 2(1/4) or 1/3 + Cr = 1/2. Hope this helps, but definitely reply if you have more questions!