Peter can drive to work via the expressway or via the backroads, which

Clearly C.
First statement gives two inputs, one the distance of the backroad one way is 30m as the roundtrip takes 1 hour at 60mph and two the speed of the commuter is 60mph. Not enough to calculate the time taken to travel on expressway. Hence insufficient.
Second statement clearly mentions the time taken to travel on expressway but no mention of the backroad. Hence insufficient.
Combining 1 and 2 we get travelling time for both the backroad and expressway and hence we can calculate the difference. Sufficient. Hence Answer is C

We have to find out the difference in the time Peter would spend driving to work via the expressway versus the backroads ?
Statement 1 gives us the information about speed on both routes,but gives us time only for travel to and fro for the backroads route
We don't have any info on time required to travel on expressway so insufficient
Statement 2 gives the information about time required to travel to and fro on the expressway. We don't have any info on time required to travel on backroads. so insufficient

Combining both statements we get the speed on both routes and also the time required on both routes. So sufficient
Correct Answer - C

P.S. don't calculate the actual difference in time in the exam and waste precious time

On this question, we will have to find a difference in the time taken by Peter while driving on two different routes.

The equation to find out time is,
Time = \(\frac{Distance }{ Speed}\).
As such, we will need the information about the distance and the speeds to be able to find the times and hence the difference. With this in mind, let us analyse the statements.

From statement I alone, we know that Peter drives at 60 mph regardless of the route. We also know that the round trip took him an hour. Therefore, the one-way distance to work should be 30 miles, when using the back roads. However, do we know that it’s the same distance when using the expressway as well? Clearly not.
That’s why, statement I alone is insufficient. Answer options A and D can be eliminated. Possible answer options are B, C or E.

From statement II alone, we know the total time spent by Peter when he takes the expressway. No information about what happens when he uses the back roads.
Statement II alone is therefore insufficient. Answer option B can be eliminated. Possible answer options are C or E.

Combining the data from statements I and II, we have the following:
From statement I, we know that Peter travelled for a total of 60 minutes; from statement II, we know that he travelled for 2/3rd of an hour i.e. 40 minutes. This is enough to calculate the difference between the two times.

Statement I and II are sufficient when taken together. Answer option E can be eliminated.
The correct answer option is C.

Note that, when you combine the statements, you do not have to worry about the distance travelled by him when using the expressways. Clearly, finding it out would only set you back in terms of time; as long as you know the times taken in both cases, why would you want to find the distance travelled on the expressway, because, remember that you are trying to find the difference in the times.

Hope that helps!

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