In a race, there are 100 bikes, consisting of yellow and green bikes. The average speed of all the bikes is 35 km/hr. The average speed of the yellow bikes is 55 km/hr, and the average speed of the green bikes is 30 km/hr. How many of the bikes are green?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 80.
Let green bikes = x
Then yellow bikes = 100 − x
Average speed equation:
(30x + 55(100 − x)) / 100 = 35
⇒ (30x + 5500 − 55x) / 100 = 35
⇒ (5500 − 25x) / 100 = 35
⇒ 5500 − 25x = 3500
⇒ 25x = 2000
⇒ x = 80