History1 min ago
Mensa Question Here.
48 Answers
A helicopter covers its outward journey at 330 mph. It returns over exactly the same distance at 165 mph. What is the helicopters average speed over the entire journey? The answer is 220, but how? I got these cards fun, but some are really hard! Thank you for your answers.
Answers
the length of the journey is irrelevant, that's the point of the question, to realise what are the salient factors, this is not primarily about the arithmetic. The journey back always takes double the journey there, let's call the distance D, the average speed A and the Time T, so the total journey takes 3T thus: A=2S/3
09:52 Fri 12th Mar 2021
davebro ASSUMED the first flight took 1 hour so, at 590mph it must have been 590 miles. The return flight is the same distance, so total distance travelled is 590 + 590 = 1180 miles.
The time for the second flight is 590/speed = 590/393.33 hours.
Total time is 1 hour + 590/393.33 hours to travel 1180 miles.
The time for the second flight is 590/speed = 590/393.33 hours.
Total time is 1 hour + 590/393.33 hours to travel 1180 miles.
Oh the poster Etch!!!
Someone on previous page gave the clear formula for working out average speed. It's total distance divided by total time. It works easily in this example only because obviously speed one way was exactly double the other so there are 3 lots of the same time to do the whole journey.
Someone on previous page gave the clear formula for working out average speed. It's total distance divided by total time. It works easily in this example only because obviously speed one way was exactly double the other so there are 3 lots of the same time to do the whole journey.
// We all allready agreed on that Peter.//
yes bobo BUT so often
there is note to my answer than the answer - - -
there is a 3x3 matrix nestling down there
also works for - - - density - mass - volume
p1 m1 v1 etc
( 2g of density 3.5g/ml and 5 mls of density 4g/ml makes a mixture of density what AND....
copes with what is the new density if there is an overall contraction of volume of 10% )
which I dont think - - - you agreed on
yes bobo BUT so often
there is note to my answer than the answer - - -
there is a 3x3 matrix nestling down there
also works for - - - density - mass - volume
p1 m1 v1 etc
( 2g of density 3.5g/ml and 5 mls of density 4g/ml makes a mixture of density what AND....
copes with what is the new density if there is an overall contraction of volume of 10% )
which I dont think - - - you agreed on
// Am I missing something here?//
yup me ( said that, not you must be missing me)
of dist, speed time - you only need two given to define the third ( two degrees of freedom BUT that is a bit advanced for 2' skool)
so if you do a speed - dist - time matrix
first part of the journey sp---d-----time and so on with the rows
you fill in all the spaces with the info given and then can sum it
here you have to realise that the Distance D or X is not given but so long as it is the same froo-out, it will cancel in this calculation
and I have to thank Mr Townend of Downside school for the matrix idea which he taught us in 1965
yup me ( said that, not you must be missing me)
of dist, speed time - you only need two given to define the third ( two degrees of freedom BUT that is a bit advanced for 2' skool)
so if you do a speed - dist - time matrix
first part of the journey sp---d-----time and so on with the rows
you fill in all the spaces with the info given and then can sum it
here you have to realise that the Distance D or X is not given but so long as it is the same froo-out, it will cancel in this calculation
and I have to thank Mr Townend of Downside school for the matrix idea which he taught us in 1965