DrMock
This was the very first question I got in my mock 6 (and I start with quant). Was this an outlier or does GMAC rate problems differently?
Hi
DrMock!
Not sure what you mean by an outlier? Usually the first question you see is going to be a somewhat middle-level difficulty, but that isn't exact! Let me know what makes you think this might be an outlier?
thr3at
Hello,
Can you please correct me where I am wrong.
Combined efficiency of the pipes ( in and Out) per hour = 14/24 (14g every 24 hours) - 1/4 ( ever hour gallons of water removed)
= 1/3
We have to fill 14G of water (46.75 - 32.75)
Time (in Hours)= 14/0.33= 42
In terms of days= 42/24=~ 1.8
1.8 days = 1 day + 18 hours.
Please correct me where I am wrong.
ndwz
same doubt.. can someone please explain why we don't add 42 hrs to 2PM Tuesday to get an answer of 8AM Thursday
The issue is that you're considering the once-a-day fill in as an hourly change, which it isn't. That 14 gallons hits the tank all at once at 1pm each day, not little by little throughout the day the way the leak is occurring (0.25 gallons / hour = 6 gallons for each 24 hour period. So you can't roll the two together into one step - you must treat this problem step by step!
I actually also found this easier if I backed up from 2pm on Tuesday to 1pm on Tuesday (since that's the moment that we add the 14 gallons each day). I also like to use the answer choices rather than being precise at first!
Tuesday 1pm = Tues 2pm + the 0.25 gallon that was lost in the hour = 32.75 + 0.25 = 33 gallons.
Tues 1pm = 33 g
Wed 1pm = 33 - 6 + 14 = 41 g
What can we eliminate now? We are still lower than 46.75 but for the next 24 hours we're just going to keep dropping... so we won't have another shot at getting an add until Thursday at 1pm. We can eliminate A, B, and C - since those are all before Thursday at 1pm.)
Thu 1pm = 41 - 6 + 14 = 49 g
What can we eliminate now? We've overshot, meaning, we need to lose gallons and not get another add. So we could eliminate anything from Friday 1pm onwards, but that isn't an option.
From 49g we need to lose just over 2.25 gallons = 9 hours later, or 10pm!
Hope this helps!

Whit