A man drove for 4 hours at a certain speed, he then doubled his speed and drove for another 3 hours. Although he covered 600 kilometers. At what speed did he drive for the last 3 hours?
A
120km/hr
B
60km/hr
C
670km/hr
D
40km/hr
Verified Correct Answer: A.
Step-by-Step Mathematical Solution
Speed = \(\frac{distance}{time}\)
let x represent the speed, d represent distance
x = \(\frac{d}{4}\)
d = 4x
2x = \(\frac{600 - d}{3}\)
6x = 600 - d
6x = 600 - 4x
10x = 600
x = \(\frac{600}{10}\)
= 60km/hr
Since speed was doubled for the last three hours = 2 x 60km\hr = 120km\hr.
Source: Myschool Past Questions Archive (Record #32480)