Data Sufficiency

How many hours did it take Helen to drive from her house to her parent's house?

1) Helen's average speed on this trip was 72 kilometers per hour.

2) If Helen's average speed on this trip had been 8 kilometers per hour greater, it would have taken her 1 hour less.

Thanks!

Let us assume, Helen's average speed was v kilometer per hour and the distance between her house and her parent's house is d kilometers.
So, time taken t = d/v hours

Statement 1: No information about d.
So, statement 1 is not sufficient

Statement 2: If her average speed was (v + 8) kmph, she would've taken (t - 1) hours to cover the distance.
So, vt = (v + 8)(t - 1)
So, vt = vt + 8t - v - 8
So, t = (v + 8)/8
As we don't know v, we can't determine t.
So, statement 2 is not sufficient

Both together: t = (v + 8)/8 and v = 72
So, we can find t.
So, both statements together is sufficient

Answer : C