Big Book Test 2 Section 5 (Question 29)

[Archi]

I am sorry for asking so many questions but this one I mostly get wrong. Here in the equation I put relative speed as (x-2). x being the rate of outflow of spout B and 2 being the flow rate of spout A. Now, my equation looks like this-

64 = (x-2)96
This gave me an answer of 8/3 but the correct answer is 4/3 and 4/3 will be obtained if relative speed is (2-x) but my question is why would it be like this? As spot A is filling up 64 gallons in just 32 hours so in order for us to delay it to 96 x has to be greater than 2 right?

I would also be thankful if you could tell me if there is any solution class Greg has done for this. I would really like to attend it to strengthen my concept because I have watched the foundation video for it but when it comes to the application of the concept, I really mess up

[Max]

It might help to visualise this

Water is running in and out of this container, and in 96 hours it will be full

The total capacity is 64 gallons

We’re asked to find the rate of outflow from the drum

We’re give the rate of inflow as 2 gallons/hr

A simple way to think about this is;

In 96 hours; the total amount of inflow - the total amount of outflow = 64 gallons

After that it’s just plugging in the values

2 gallons/hr X 96 hrs = 192gallons total inflow

Total outflow = 192 - 64 gallons = 128gallons

Rate of outflow = 128/96

Simplified = 4/3

I’ll get back to you regarding the video request

[Archi]

Right but I often get confused in determining which would be a bigger value in relative speed so I would be thankful if you could share some resources to practice that. Your explanation makes a lot of sense. Thank you so much!