Data Sufficiency

How much time did it take a certain car to travel 400 kilometers?

1) The car traveled the first 200 kilometers in 2.5 hours.

2) If the car's average speed had been 20 kilometers per hour greater than it was, it would have traveled the 400 kilometers in 1 hour less time than it did.

Stmt 1 :
not sufficient.
we know nothing of how the car travelled the remaining distance.

Stmt 2:
Sufficient.
Let speed =x
distance is 400
400/x = 400/x+20 + 1
Can be solved for x and thus we can get the time taken.

B

st(1) The car traveled the first 200 kilometers in 2.5 hours Not sufficient, as we don't know time spent on the remaining 200 km.
st(2) If the car's average speed had been 20 kilometers per hour greater than it was, it would have traveled the 400 kilometers in 1 hour less time than it did -> s=speed and 400/s -1=400/(s+20)
(400-s)(s+20)=400s, 400s-s^2-20s+8000=400s <> s^2+20s-8000=0, (s+40)(s-20)=0, s{20,-40}
speed can be only +ve no, hence s=20 Sufficient. Time=400/20 or 20 hours

IOM b