For the 'varying speed' scenario, we need to know the relative percentages of the 40 miles that were spent driving at X mi/hr vs. driving at 1.25X mi/hr. Without even inserting numbers for proof, there's a huge difference between driving for 1 mile at X mi/hr (39 miles at 1.25X mi/hr) and driving 39 miles at X mi/hr (1 mile at 1.25X mi/hr). We need to know the value of 'Y'.

Statement (1) is insufficient

Given the value of Y=20, I chose numbers which were useful for testing.
Say x=80 mi/hr, so 1.25X = 100 mi/hr.

Driving the first 20 miles at 80 mi/hr requires a driving time of 1/4 hr.
Driving the other 20 miles at 100 mi/hr requires a driving time of 1/5 hr.
Total driving time = 1/4 + 1/5 = 9/20 hrs

If the entire trip is made at X (80) mi/hr, a driving time of 1/2 hr is required.

We want to know the ratio: (Time required to drive 20 miles @ 80 mi/hr and 20 miles @ 100 mi/hr)/(Time required to drive 40 miles at 80 mi/hr)
This equals (9/20) / (1/2) = 9/10.

Statement (2) is sufficient.

Ans: B