This puzzle courtesy of © Kevin Stone [www.brainbashers.com]
A plane maintains an average speed of 696mph from London to New York. It then returns from New York to London at an average speed of 145mph. What is the average speed for the entire journey?Will post the answer in a day or two
Answer:
240mph: let the distance be x miles. Therefore, the outward trip takes x / 696 hours and the return trip takes x / 145 hours. The total distance travelled is hence 2x, in a time of (x / 696 + x / 145). Therefore the speed (distance / time) is given by 2x / (x / 696 + x / 145) = 240 mph. QED.
The average speed, from point A to point B and back to point A cancels out to 0mph.
B Selande, that’s average velocity you’re thinking of. Speed is not a vector quantity. http://www.glenbrook.k12.il.us.....U1L1d.html
ok well i’m positive your wrong dr kap,
well let me think
well d=distance
t=time
s=speed
as d/t=s if ya don’t believe me google it
we have d/t=696 and d/t=145 or d=696t and d=145t so then just add them and get 2d=841t then divide by 2 so d=420.5t so therefore s=d/t making the answer 420.5mph as the average,
Ok now lets see if i can disprove the firsts guy theory,
ok so he’s saying t/696=d and t/145=d which is the same as what i said originally so he should get the same answer as me but
now this guys getting confused with distance and time in his equation and he gets 240mph as his answer which doesn’t even make any sense
“Hmmm”- since you list d/t twice (one for each plane), don’t we have to list d1/t1 and d2/d2?