Do you have an explanation for your answer? I arrived at A because it says suresh travelled from 1am to 1pm "yesterday". So all the travelling was done yesterday and he travelled for 13 hours "yesterday".

How many hours did Suresh travel yesterday?

(1) Yesterday, Suresh traveled from 1 A.M. to 1P.M. without a break.
Tricky, very tricky. It's possible that she (he?) traveled from 1AM to 1PM (12 hours) or from 1 AM to 1 PM to 1 AM. (24 hours) Let's say she started Sunday morning at 1AM and drove to 1PM Sunday afternoon and drove from 1PM to 1AM Monday morning. Monday afternoon it is acceptable to say that "she drove 24 hours yesterday" even if she finished the morning of the day you made that statement.
INSUFFICIENT

(2) Yesterday, Suresh traveled half the total number of hours he traveled the day before yesterday.
To make it easier, let's say yesterday was Sunday meaning the "day before yesterday" was Saturday. This means if Suresh drove 12 hours on Sunday he drove only 6 on Saturday. Still, we don't know how many hours he traveled.
INSUFFICIENT

1+2) Suresh traveled either 12 or 24 hours yesterday. Suresh is on a 12 hour cycle meaning that if he were to travel on Sunday he would have had to travel 1AM-1PM (12 hours) He would have had to travel a total of 24 hours on Saturday to double that figure.

(C)

I think my logic on this problem is shaky at best. Could someone give a more in depth explanation?

Thanks!

Hi ssriva2,

One of the 'keys' to this question (and all DS questions) is to be a bit cynical about the information that you've been given. Think about what you KNOW and what you DON'T KNOW and be prepared to do the necessary work to find any patterns that exist in the information.

In this prompt, we're asked for the number of hours that Suresh traveled yesterday. We're given no information to start with, but we DO know that he could not have traveled for more than 24 hours (because there's only 24 hours in a day).

Fact 1: Yesterday, Suresh traveled from 1 A.M. to 1P.M. without a break.

This tells us that Suresh traveled for AT LEAST 12 hours. He COULD have traveled for some additional time before 1am or after 1pm, so we don't know how many hours he traveled on that day in total.
Fact 1 is INSUFFICIENT

Fact 2: Yesterday, Suresh traveled half the total number of hours he traveled the day before yesterday.

This doesn't give us any direct numbers to work with, but it DOES establish a ratio. The time spent traveling yesterday was HALF what it was the day before yesterday. This means that Suresh could have traveled AT MOST 12 hours (since there are only 24 hours in a day, and HALF of that is 12 hours), but we still don't know the exact number of hours traveled.
Fact 2 is INSUFFICIENT

Combined, we know.....
Suresh traveled AT LEAST 12 hours
Suresh traveled AT MOST 12 hours

These Facts tell us that Suresh must have traveled exactly 12 hours.
Combined, SUFFICIENT

Final Answer:

GMAT assassins aren't born, they're made,
Rich
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How are we arriving this at least statement from 1?