A little math quiz

BOBBO · 13th February 2007

Here is an interesting little math problem.

A man drives a car for one mile at 60 miles per hour and for another mile at 120 miles per hour. What is his average speed?

**ReggieB** · 13th February 2007

That looks to me like 60 seconds at 60 mph and 30 seconds at 120 mph. 90 seconds total travel.

Total speed = (60*(60/90))+(120*(30/90))

So 80 mph I think.

**ReggieB** · 13th February 2007

Or if you don't like that method:

Total travel is 2 miles in 90 seconds.
So 1 mile in 45 seconds. (divide by 2)
0.022222 miles per second. (1 / 45)
1.33333 miles per minute. ((1/45)*60)
And 80 mph. (((1/45)*60)*60)

**TonyT** · 14th February 2007

average speed was 80 mph

average mph is calculated as such:
total miles divided by time.

if I drove 100 miles and it took me 2 hours then my average speed was 50 mph.

in this case he drove 2 miles and it took him 90 seconds
or
he drove 2 miles and it took hime 1.5 minutes
or
he drove 2 miles and it took him .025 hrs

2 divided by .025 = 80 mph

BOBBO · 14th February 2007

Interesting how different people come up with different procedures. One of my friends said:

Car traveled 2 miles / 1.5 min (first mile took 1.0 minutes, the second took 0.5 minutes) = average speed in miles/minute. So 2/1.5 miles per min multiplied by x/60 gives miles per hour. x = 80 mph

Another friend explained it this way:

He drives 2 miles in 1.5 minutes, so his average speed is (2/1.5) x 60 = 80mph.

**TonyT** · 15th February 2007

I have another way to demonstrate it....but my truck won't go 120 mph!

**ReggieB** · 17th February 2007

Quote:

Originally Posted by TonyT

I have another way to demonstrate it....but my truck won't go 120 mph!

The best answer so far!!!!

I expect your van also can't accelerate from 60mph to 120mph instantaniously.

**TonyT** · 19th February 2007

Quote:

Originally Posted by ReggieB

The best answer so far!!!!

I expect your van also can't accelerate from 60mph to 120mph instantaniously.

more likely once it hit 105 it would rapidly decelerate in a puff of clangs and smoke.