Solutions

Question

A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

 

Difficulty Level

Hard

Solution

Option B is the correct answer.

Option Analysis

75 kilometers per hour is the same as 75 kilometers per 60 minutes….

75/60 = 5/4 = 5 kilometers every 4 minutes

This means that every 1 kilometer takes 4/5 minutes = 48 seconds

We’re then asked to add 2 seconds to this and calculate the speed. 48 + 2 = 50 seconds

To find the speed, we can use a ratio (50 seconds = 5/6 minutes):

5/6 = 60 min/X kph

Cross multiply the ratio: 5X = 360

X = 72 kph