changhiskhan
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.
First, write what we are solving for: "T?"
(1) R = 72 --->
Insufficient (We would also need the distance to solve for time ---> Using D=RT, we could get T = \(\frac{D}{R}\) =\(\frac{D}{72}\), but we have 2 variables and one equation)
(2) We translate the "If..." statement, saying the hypothetical distance is equal to the actual distance:
RT = (R+8)(T-1)
Again, 2 variables and 1 equation --->
Insufficient(1) & (2) Together: Now, we have 2 variables and 2 equations -->
Sufficient ---> Answer is
C (or, once you plug in R = 72 into statement 2, we just have one linear equation and one variable)
For another similar example of this "If..." wording, try this one:
https://gmatclub.com/forum/a-store-curr ... l#p1161554