Question

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?

• A. 50
• B. 80
• C. 65
• D. 70

Answer 1

Answer:

B. 80

Let the number of green bikes = x
Then yellow bikes = 100 − x

Using weighted average:

$\frac{55(100 - x) + 30x}{100} = 35$

$55(100 - x) + 30x = 3500$

$5500 - 55x + 30x = 3500$

$5500 - 25x = 3500$

$25x = 2000$

$x = 80$

Answer: 80 green bikes