# Average speed question

• Dec 12th 2009, 02:27 AM
Mukilab
Average speed question
A delivery lorry covers its outward journey at 50mph.
It returns, over exactly the same distance at 33.3333mph.
What is the lorry’s average speed over the entire journey?

Not allowed to use a calculator. I would place the common denominator as 99.99999 or 100, bt is there any better denominator than this?
• Dec 12th 2009, 02:39 AM
mr fantastic
Quote:

Originally Posted by Mukilab
A delivery lorry covers its outward journey at 50mph.

It returns, over exactly the same distance at 33.3333mph.

What is the lorry’s average speed over the entire journey?

Not allowed to use a calculator. I would place the common denominator as 99.99999 or 100, bt is there any better denominator than this?

$t = \frac{x}{50} + \frac{x}{33 \frac{1}{3}} = \frac{x}{50} + \frac{3x}{100} = \frac{5x}{100} = \frac{x}{20}$.

Now do exactly what you have been shown in another thread.
• Dec 12th 2009, 08:23 AM
Mukilab
Done.