Car speeds

[coolgirl26]

I don't get it

why is 2 correct

can someone show how to solve to find the time as per statement 2

[skris79]

1) Statement 1 is not sufficient as we know only abt the first 200 Km
2) Time = Distance/Speed
using the second statement we get (let time be t and avg speed be x)
t = 400/ x
t-1 = 400/ (x+20)
solve this 2 equations and you get the time. So statement 2 alone is sufficient.