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Once: win one of two Mensa Brain Trainer hand held consoles

7y, 1m agoFound 7 years, 1 month ago / ended 30 Sep 0930 September 2009
Product:
win one of two Mensa Brain Trainer hand held consoles
Period:
Once
Availability:
Online
this ones a good tester

A helicopter covers its outward journey at 322 mph.
It returns, over exactly the same distance at 241.5 mph
What is the helicopters average speed over the entire journey?

For a chance to win one of two Mensa Brain Trainer hand held consoles, simply e-mail the correct answer together with your full name and address to the Puzzle Editor

I make the answer 2*(241.5*322)/(241.5+322) = 276mph.
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7y, 1m agoFound 7 years, 1 month ago / ended 30 Sep 0930 September 2009
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(7)
#1
surely you just add both and then divide by 2?
i make it 281.75
#2
entered, thanks
#3
wow, that took all of 2 seconds.
try this one
If birmingham is 26 miles from your position, burnley is 50 miles, bradford is 8 miles. How far is blackpool?
#4
brooke007bond
Hi, I believe the answer is 281.75
to find the average speed you add the two speeds then divide by two.
322 + 241.5 = 563.5, 563.5 / 2 = 281.75

That's the common mistake people make with this sort of problem. Speed=distance/time (s=d/t). You can rearrange the equation to t=d/s

For the outward journey, the time taken is equal to 322/distance. On the return journey, the time taken is equal to 241.5/distance. This makes the total time of the journey 322/d + 241.5/d. If the total distance travelled on the journey is 2d, the average speed is 2d/[(322/d)+(241.5/100)] = 276mph
#5
Can anyone give me the e'mail address of the Puzzle Editor, my laptop will not open a direct link
#7
Thanks