maths based riddles... See if you can answer them.

[Du1point8]

So many maths based riddles that I thought I would start a new thread for them all as a little game were the person who answers with the correct answer gets to ask the next one...

I had some fun confusing my friends last night with this little one that they couldnt get their head round.

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If you have a one mile race track and you must complete two laps, for a total of two miles.

no more, no less.

If you average 30mph on the first one mile lap, how fast would you have to go on the second lap to average 60 MPH?

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I await the first smart arsed comment.

[MX7]

90

[Einion Yrth]

It can't be done.

[Oldandslow]

You cannae break the laws of physics, Cap'n

[okgo]

90?

[illmonkey]

Stupid wording:

To average 60MPH on the second lap, its 60mph.

To average 60MPH over both laps, its 90MPH on the second lap.

[Slinky]

MX7 said:

90

Two lap total has to be 120 for a 1 lap average to be 60..

[Du1point8]

illmonkey said:

Stupid wording:

To average 60MPH on the second lap, its 60mph.

To average 60MPH over both laps, its 90MPH on the second lap.

How do you work that?

Since many have it I will explain why its not possible by answering 90mph.

Since it has already taken 2 minutes to cover 1st mile and you cant cover the 2nd in 0 time, doing it at 90mph would take 40 seconds, which would mean it just took you 2mins 40s to cover 2 laps or an average of 45 mph.

Edited by Du1point8 on Monday 15th August 12:15

[530dTPhil]

Can't be done. One mile at 30mph takes two minutes. To average 60 mph for the whole two miles would take two minutes, i.e. the time already elapsed.
As has been said, can't deny the laws of physics, even in a remapped 335d!

[Einion Yrth]

Two miles and two miles only. To average 60 over the course of two miles I have to complete the course in 2 minutes. I have already taken two minutes doing the 1st lap at an average of 30. Ergo I am out of time and it cannot be done.

[illmonkey]

Du1point8 said:

illmonkey said:

Stupid wording:

To average 60MPH on the second lap, its 60mph.

To average 60MPH over both laps, its 90MPH on the second lap.

How do you work that?

It could read as a 'trick' question.

You said:

how fast would you have to go on the second lap to average 60 MPH?

Might read as how fast on the second lap do you need to go to average 60MPH on the second lap.

Where does it mention the 2 minute rule?

[andy400]

Unless, of course, you called the 30mph for Lap 1 the average speed of the lap, then did 90mph for lap 2. Then worked out your average speed, lap by lap, by the simple method of 90+30 / 2 in which case it would be 60mph.

Did I make sense? Probably not, I rushed it as I'm in the middle of something I actually get paid for. Someone will see what I'm getting at........

Hopefully

[jeremyc]

The Pure rather than Applied Maths answer is of course: infinitely quickly (which will get you round in 0 seconds).

[Mattt]

Can be done.

You just need to travel infinitely quickly on the second lap, therefore 2 minute total time.

[Einion Yrth]

andy400 said:

Unless, of course, you called the 30mph for Lap 1 the average speed of the lap, then did 90mph for lap 2. Then worked out your average speed, lap by lap, by the simple method of 90+30 / 2 in which case it would be 60mph.

Did I make sense? Probably not, I rushed it as I'm in the middle of something I actually get paid for. Someone will see what I'm getting at........

Hopefully

Read. the. thread.

[Einion Yrth]

Mattt said:

Can be done.

You just need to travel infinitely quickly on the second lap, therefore 2 minute total time.

Cannot exceed (or even reach) the speed of light (about 186000 miles per second).

[DrTre]

2 mins?

Eta am a 'tard

[Big Rod]

illmonkey said:

Might read as how fast on the second lap do you need to go to average 60MPH on the second lap.

Where does it mention the 2 minute rule?

Took me a bit to get my head around that too, but to average 60 MPH over the whole, (2 miles), course you'd have to do it in 2 minutes. As you've already taken two minutes to do your first lap then you can't average 60 MPH as you've already used the time it'd take you to achieve the average.

I'm not sure that made sense out loud, but the voices in my haed say it's right.

[Du1point8]

I hate these questions in interviews and have had to do so many...

Next one is up to you guys so I open up the floor for someone else to ask one.

[Guffy]

Du1point8 said:

Next one is up to you guys so I open up the floor for someone else to ask one.

So... if an aeroplane was on a giant conveyor belt that matched the speed of it, but in the opposite direction, could it take off....