BTGModeratorVI wrote: ↑

Mon Sep 14, 2020 8:35 am

If the capacity of tank X is less than the capacity of tank Y and both tanks begin to fill at the same time, which tank will be filled first?

(1) Tank X is filled at a constant rate of 1.5 liters per minute.
(2) Tank Y is filled at a constant rate of 120 liters per hour.

Answer: E
Source: Official guide

Given: The capacity of tank X is less than the capacity of tank Y and both tanks begin to fill at the same time

Target question: Which tank will be filled first?

Statement 1: Tank X is filled at a constant rate of 1.5 liters per minute.
Since we have no information about the rate at which tank Y is filled, statement 1 is NOT SUFFICIENT

Statement 2: Tank Y is filled at a constant rate of 120 liters per hour.
Since we have no information about the rate at which tank X is filled, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that tank X is filled at a constant rate of 1.5 liters per minute.

Statement 2 tells us that tank Y is filled at a constant rate of 120 liters per hour
In other words, tank Y is filled at a constant rate of 120 liters per 60 MINUTES
In other words, tank Y is filled at a constant rate of 2 liters per MINUTE

We can see that tank Y is filled at a faster rate that tank X is filled.
However, since tank Y has a greater volume that tank X, it's impossible to determine which tank gets filled first.

To better understand what I mean, consider these two possible cases:
Case a: Tank X holds 15 liters and tank Y holds 16 liters.
Time to fill a tank = (tank's volume)/(rate)
So, time to fill tank X = 15/1.5 = 10 hours
Time to fill tank Y = 16/2 = 8 hours
In this case, the answer to the target question is tank Y is filled first

Case b: Tank X holds 1.5 liters and tank Y holds 16 liters.
Time to fill a tank = (tank's volume)/(rate)
So, time to fill tank X = 1.5/1.5 = 1 hour
Time to fill tank Y = 16/2 = 8 hours
In this case, the answer to the target question is tank X is filled first

Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

Cheers,
Brent