Complete question is;
There are three different hoses used to fill a pool: hose x, hose y, and hose z. Hose x can fill the pool in a days, hose y in b days, and hose z in c days, where a > b > c. When all three hoses are used together to fill a pool, it takes d days to fill the pool. Which of the following must be true?
I. d < c
II. d > b
III. c/3 < d <a/3
A) I only
B) III only
C) I and III only
D) II only
E) I, II and III
Answer:
The correct option is C
Step-by-step explanation:
From the question, the 3 hoses combined together will fill the pool faster than the time for the hoses to accomplish it individually. Therefore, the time "d" will be lesser than any of the individual times used by each hose.
Hence, statement I is true and II is false.
Now, we know that if each of the three hoses took c days to complete the job, then together they would take c/3 days. However, in reality, two of the three hoses even took more than c days. So, in a nutshell together they would take more than "c/3" days, and therefore d > c/3.
Likewise, if each of the three hoses took "a" days to finish the job, then when combined together, they would take "a/3" days. Now, two of the three hoses used fewer than "a" days and so when combined together they would take less than "a/3" days and therefore d < a/3.
If we combine the last 2 paragraphs, we will arrive at c/3 < d < a/3 and that is same as statement III.
Thus, statement I and III are true. The correct option is C
