A car, during its entire journey of 5 hours, travels the first 45 minutes at a certain speed, the next 75 minutes at a speed of 85 km/h, and the last 3 hours at a speed of 70 km/h. During its entire journey, the average speed of the car is found to be 73 km/h. What is the speed (in km/h) of the car during the first 45 minutes?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 65.
Given that
The time of entire journey = 5 hours
Let a car travels the first 45 minutes at a certain speed of X km/h
The next 75 minutes at a speed of 85 km/h, and the last 3 hours at a speed of 70 km/h
The average speed of the car during whole journey = 73 km/h
Formula used
Total Distance = Average speed × total time
According to the question
⇒ 45X/60 + 75 × 85/60 + 3 × 70 = 73 × 5
⇒ 45X/60 + 106.25 + 210 = 365
⇒ 45X/60 = 365 - 316.25 = 48.75
⇒ X = 48.75 × 60/45 = 65 km/h