A coach took a class on an excursion to Mt Isa. It left the school at 7.30 am and arrived at 2.15 pm. It travelled along minor roads at an average speed of 60 km/h for the first quarter hour and the last half hour of the trip. For the rest of the trip the bus drove along highways and had a higher average speed. The bus stopped between 12.10 pm and 1.10 pm for a lunch break. If the trip was 495 km long, what was the average speed of the bus while travelling along the highways?

To find the average speed of the bus while traveling along the highways, we need to first calculate the total time spent on minor roads and the total time spent on highways.

The total time spent on minor roads can be calculated by adding the time spent during the first quarter hour and the last half hour of the trip:

Time spent on minor roads = 15 minutes + 30 minutes = 45 minutes

Next, we need to calculate the total time spent on the trip. The trip started at 7.30 am and arrived at 2.15 pm, which means the duration of the trip is:

Total time spent on the trip = (2:15 pm - 7:30 am) = 6 hours and 45 minutes = 405 minutes

We also know that the bus stopped between 12:10 pm and 1:10 pm for a lunch break, which means the lunch break lasted:

Lunch break duration = (1:10 pm - 12:10 pm) = 60 minutes

Now, we can calculate the total time spent on highways by subtracting the time spent on minor roads and the lunch break duration from the total trip duration:

Time spent on highways = Total time spent on the trip - Time spent on minor roads - Lunch break duration
= 405 minutes - 45 minutes - 60 minutes
= 300 minutes

Finally, to find the average speed of the bus while traveling along the highways, we divide the total distance traveled on highways by the time spent on highways:

Average speed on highways = Distance traveled on highways / Time spent on highways
= 495 km / 300 minutes

First, we need to convert the time spent on highways from minutes to hours:

300 minutes / 60 minutes/hour = 5 hours

Now we can calculate the average speed:

Average speed on highways = 495 km / 5 hours

Answer: *Average speed on highways = 99 km/h*