Go fetch it, Rufus . . . he's a dog, of course

[Ossy]

An bit of mental maths, whilst you're finishing your toast.

 

Rufus the dog takes 4 minutes to run the 1 km to the newsagents, against the wind, and 3 minutes to return, with the wind.

How long would it take Rufus to fetch your paper, if no wind?

 

It's 9:07 am and your time starts . . . NOW

[nausea]

The same.

[Ossy]

6 hours ago, nausea said:

The same.

Sorry, Nausea . . . been tied up, but must sadly inform of a wrong answer. Don't worry though . . . I reckon most attempts will say the same. It's a good one, let me warn you

[nausea]

I await the correct answer with interest.

[Ossy]

1 hour ago, nausea said:

I await the correct answer with interest.

OK, Nausea, since you're the only puzzler to have a go, here it is, workings included:-

 

RTF:     How long, one way, if no wind?  Easy to assume that 3½ mins is the correct answer, but think again

 

Method:

You need to accept that, although time is the initial unit of measure of Rufus’s travels, the governing factor, relating to a wind-less trip, is not time, but speed. The workings are:-

Time difference   =    1 min, therefore wind affects time at ½ min/km, giving outward and return speeds of 15kph and 20 kph, i.e. 60/4 and 60/3, respectively, and therefore . . .

Speed diff.            =     5kph, therefore wind effects speed at 2½kph, each way.

It follows that, without 2½kph wind effect, Rufus’s speed would be 17½kph and, therefore, that

time taken, with no wind, would be 60/17½ mins = 3.42857 minutes or 3 minutes: 25.7 seconds  (6.85714 mins or 6 mins: 51.4 secs for 2-way) and not the more ‘obvious’ 3½ minutes

 

A little good'un, eh?

[Crossy]

21 hours ago, Ossy said:

6.85714 mins or 6 mins: 51.4 secs for 2-way

As an engineer, that's pretty darn close to the "obvious" 7 minutes (2% difference). Certainly within the limits of experimental error.

 

[nausea]

On 05/10/2017 at 9:29 PM, Ossy said:

OK, Nausea, since you're the only puzzler to have a go, here it is, workings included:-

Yeah, I suspected the intuitive answer would be wrong; too easy. If you're interested in these counter intuitive solutions take a look at the Monty Hall problem:

 

 

Took me a while to get my head around that one, but I got it eventually. The key thing here is not knowing the correct answer, but understanding why it's the correct answer.

Edited October 6, 2017 by nausea
More info.

[Ossy]

8 hours ago, nausea said:

Yeah, I suspected the intuitive answer would be wrong; too easy. If you're interested in these counter intuitive solutions take a look at the Monty Hall problem:

 

 

Took me a while to get my head around that one, but I got it eventually. The key thing here is not knowing the correct answer, but understanding why it's the correct answer.

Thanks, Nausea. I'll wait 'til I have a few minutes of 'nothing-else-ness', before pressing 'go'