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Speed question - maths

Please refer to attachment.

If the normal route of 4 nm takes 2 hours and the boat sails 75% slower then I'd assume you could just do:

1.75x2hous = 3hours

But this is incorrect
(edited 3 years ago)
75% slower question .png201.1KB
Original post by As.1997
Please refer to attachment.

If the normal route of 4 nm takes 2 hours and the boat sails 75% slower then I'd assume you could just do:

1.75x2hous = 3hours

But this is incorrect

If the boat is sailing 75% slower, it is now sailing at 25% of its original speed.
Where are you getting 1.75 from?

(And 1.75x2 =3.5)
Reply 3
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As.1997
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Original post by old_engineer
If the boat is sailing 75% slower, it is now sailing at 25% of its original speed.

It seems logical that you could also make the time (2hours) 75% longer?
Both methods make sense to me except the method I am using seems to give the wrong answer.
(edited 3 years ago)
Reply 4
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As.1997
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Original post by GabiAbi84
Where are you getting 1.75 from?

(And 1.75x2 =3.5)

If the boat is travelling 75% slower then it should take 75% longer?
Hence if the original time is 2hours then the new time should be 75% longer i.e. 1.75x2= 3.5hours
Reply 5
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As.1997
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Would appreciate any ideas or if you feel there is a flaw in my approach please do let me know
Original post by As.1997
Would appreciate any ideas or if you feel there is a flaw in my approach please do let me know
[url=https://www.thestudentroom.co.uk/showthread.php?t=6891718
(edited 3 years ago)
Original post by As.1997
It seems logical that you could also make the time (2hours) 75% longer?

The problem with that line of thinking is that time taken is inversely proportional to speed, not directly proportional.

If t1 = s/v, then t2 = s/(v(1-0.75))
(edited 3 years ago)
Reply 8
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As.1997
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Original post by old_engineer
The problem with that line of thinking is that time taken is inversely proportional to speed, not directly proportional.

If t1 = s/v, then t2 = s/(v(1-0.75))

Another flaw in my thought process was that I kept assuming that 75% slower was referring to time. By slower, it is referring to the speed.

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