For the first 1 1/2 hours of a 91km journey the average speed was 30km/h.If the average speed for the reminder of the journey was 23km/h, calculate the average speed for the entire journey.

Distance travelled for 1.5 hours at 30

= 1.5*30 km
= 45 km
Remainder of journey
= 91-45
= 46 km
Time required at 23 km/hr
= 46/23
= 2 hours
Total distance = 91 km
total time = 1.5 + 2 = 3.5 hours
Average speed
= 91/3.5 km/hr
=26 km/hr

To calculate the average speed for the entire journey, you need to find the total distance traveled and the total time taken.

Let's start by calculating the distance traveled during the first 1 1/2 hours, when the average speed was 30 km/h.

Distance = Speed * Time
Distance = 30 km/h * 1.5 h
Distance = 45 km

Next, we need to calculate the distance traveled during the remaining time. Since the entire journey is 91 km and we already traveled 45 km, the remaining distance would be:

Remaining Distance = Total Distance - Distance Traveled
Remaining Distance = 91 km - 45 km
Remaining Distance = 46 km

Now, we calculate the time taken for the remaining distance. We know that the speed is 23 km/h, so we can use the formula:

Time = Distance / Speed
Time = 46 km / 23 km/h
Time = 2 hours

To find the total time taken, we sum the time taken for the first part (1.5 hours) and the time taken for the remaining part (2 hours):

Total Time = 1.5 hours + 2 hours
Total Time = 3.5 hours

Finally, we can calculate the average speed for the entire journey by dividing the total distance by the total time:

Average Speed = Total Distance / Total Time
Average Speed = 91 km / 3.5 hours

Therefore, the average speed for the entire journey is approximately 26 km/h.