magical cook wrote:On a certain nonstop trip, Marta averaged x miles per hour for 2 hours and y miles per
hour for the remaining 3 hours. What was her average speed, in miles per hour, for the
entire trip?
(1) 2x + 3y = 280
(2) y = x + 10

average speed = total distance traveled/ time taken to travel that distance ...

the first 2 hours martha travels 2*x miles and in the next 3 hours she travels 3*y miles .. so the total distance traveled = 2x+3y..

and the time taken to travel that distance = 2+3= 5 hrs ..

so the average speed = (2x+3y)/5 ..

Now, the first statement gives the value of the numerator .. that is 2x+3y=280 .. so average speed = 280/5= 56 miles/hr ... so statement 1 is sufficient ..

statement 2 as is evident is not sufficient .. so the answer is A .. easy right ?

Indeed....it's easy! thanks for your explanation.