We are given that a certain plumber charges $92 for each job completed in 4 hours or less and $23 per hour for each job completed in more than 4 hours. We are also given that it took the plumber a total of 7 hours to complete two separate jobs, and we need to determine the total amount the plumber charged for the two jobs.

Statement One Alone:

The plumber charged $92 for one of the two jobs.

We see that the job for which he charged $92 could be 1, 2, 3, or even 4 hours long, which means the other job was 6, 5, 4, or 3 hours, respectively. Thus, we cannot determine the total amount charged for the two jobs. Statement one alone is not sufficient to answer the question.

Statement Two Alone:

The plumber charged $138 for one of the two jobs.

We see that the job for which he charged $138 must be longer than 4 hours. Since he charges $23 per hour for a job that is longer than 4 hours, we have:

138 = 23(number of hours)

6 = number of hours

Thus, the other job must have taken 1 hour, with a cost of $92. The two jobs will cost a total of $138 + $92 = $230. Statement two is sufficient to answer the question.

Answer: B
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Target question: What was the total amount charged by the plumber for the two jobs?

Given: $92 for each job completed in 4 hours or less. $23 per hour for each job completed in more than 4 hours. Total work time was 7 hours

Statement 1: The plumber charged $92 for one of the two jobs
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several scenarios that satisfy statement 1. Here are two:
Case a: the plumber spent 1 hour on one job (and received $92) and spent 6 hours on the other job (at $23/hours). In this case, the TOTAL amount charged = $92 + (6)($23) = $230
Case b: the plumber spent 2 hours on one job (and received $92) and spent 5 hours on the other job (at $23/hours). In this case, the TOTAL amount charged = $92 + (5)($23) = $207
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, read my article: http://www.gmatprepnow.com/articles/dat ... lug-values

Statement 2: The plumber charged $138 for one of the two jobs.
This means the plumber MUST have spent more than 4 hours on this job
So, the rate charged is $23/hour
$138/23 = 6. So, the plumber spent 6 hours on this job (and received $138), which means he spent 1 hour on the other job (and received $92)
So, the TOTAL amount charged = $138 + $92 = $230
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer:

Cheers,
Brent
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I - just tells us one job was done in less than 4 hours. NS.

II - tells us the exact time it took for one of the jobs. As there are only two for a given time, We can answer the question.

Answer - B

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