There are 6 variables (estimated: v1, t1, d1, actual; v2, t2, d2) in the original condition, and 2 equations (estimated: v1t1=d1, actual; v2t2=d2). Hence, the correct answer is E.

Hi Max,

why not just divide difference in distance by difference in speed? 50/50 we get 1 minute which is smaller than 10.

Also if we take test cases,

what if d1 = 500 miles, d2 = 550 miles
for v1= 100, v2=50 then t1= 5 min, t2 = 11 min. difference = 6
for v1= 100, v2=150, then t1= 3.3 min, t2 = 5 min. difference = 2.7

what if d1=500, d2=450 then
For v1 = 100, v2 = 50 --> t1 = 5, t2= 9 difference = 4
For v1 = 100, v2 = 150 --> t1 = 5, t2= 3 min difference = 2

So combining together, the time difference is smaller than 10. So both together is sufficient right?