Average speed help

[susumandrai]

A car travels a distance of 165km in 3 ¼ hours. The average speed during the first 2 ½ hours was 12km/hr less than the average speed for the rest of the journey. What was the average speed during the last ¾ hour?

I have no idea how to do this question!

 

[pappus]

A car travels a distance of 165km in 3 ¼ hours. The average speed during the first 2 ½ hours was 12km/hr less than the average speed for the rest of the journey. What was the average speed during the last ¾ hour?

I have no idea how to do this question!

1. Use the definition of speed:

\(\displaystyle \displaystyle{ \text{speed} = \frac{distance}{time}~\implies~distance = speed \cdot time}\)

2. Let v denotes the average speed of the last 45 minutes of the trip. Then you know:

\(\displaystyle \frac52 \cdot (v-12) + \frac34 v = 165\)

Solve for v.

 

[Deleted member 4993]

A car travels a distance of 165km in 3 ¼ hours. The average speed during the first 2 ½ hours was 12km/hr less than the average speed for the rest of the journey. What was the average speed during the last ¾ hour?

I have no idea how to do this question!

Start with "naming" things to be found:

the average speed during the last ¾ hour = V₂
the average speed during the first 2 ½ hour = V₁

The average speed during the first 2 ½ hours was 12km/hr less than the average speed for the rest of the journey

V₁ = V₂ - 12

Now what.....

Please share your work with us indicating exactly where you are stuck - so that we may know where to begin to help you.

 

[susumandrai]

Start with "naming" things to be found:

the average speed during the last ¾ hour = V₂
the average speed during the first 2 ½ hour = V₁

The average speed during the first 2 ½ hours was 12km/hr less than the average speed for the rest of the journey

V₁ = V₂ - 12

Now what.....

Please share your work with us indicating exactly where you are stuck - so that we may know where to begin to help you.

Cheers everybody!
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