Speed time distance - your opinion (not so much a how to!)

Discussion in 'Joining Up - Royal Navy Recruiting' started by littleshinydemon, May 25, 2009.

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  1. Hi everybody,

    I know that the matter of STD is something that has been discussed regularly and probably to death, however I wanted to ask people's opinions on doing a couple of questions as my maths is pretty weak and I am sure there is probably a faster way of doing them! As you can probably guess I am preparing for my FATS, anyway these are questions I got from the link below which I found on an earlier thread on here

    http://www.thestudentroom.co.uk/showthread.php?t=501724

    just if anyone is interested.

    So the first question is;

    You burn 30kgs of fuel per minute. How much do you use in 45 minutes?

    Now to do this I would just multiply the 30kgs by 45 - is it really that simple? (there are no answers on the site so I cant be 100% certain and as I said my maths is pretty bad).

    The next two are a little more complex;

    You have used 280kgs of fuel in the past 80 minutes. How much do you burn per hour?

    You travel 330 miles. How much have you used if you burn 160kgs an hour, if you are travelling at 220mph?

    How, in the interest of doing them as quickly as possible, would you say was the best way to do these sums as I am a bit bamboozled by them since they aren't your standard, your speed is 360mph and you go for 20 mins, what distance do you cover type question?

    Thanks to anybody that contributes to this, I am really interested to see everyones different methods, in a hope that I might be able to use one myself!

    Cheers
    N.
     
  2. 1. Yes 30x45
    2. Easiest way is probably to notice that 80 minutes is 1 1/3 hours, or 4/3. So to work it out for one hour, divide 280 by 4 then multiply by 3 (work it out as 28/4x3 then x10) - If this doesn't make sense let me know.
    3. First work out how long it takes to travel 330 miles, then same as question one for fuel consumption - I'll leave this one for you to work out properly.

    Good luck!

    Edit: You might find it easier to do 1. in two steps, multiply 30 by 9 then 5, or 45 by 6 then 5.
     
  3. witsend

    witsend War Hero Book Reviewer

    1. You have used 280kgs of fuel in the past 80 minutes. How much do you burn per hour?

    280 divided by 80 = an answer for 1 minute. Multiply this answer by 60 (minutes) = answer per hour.

    2. You travel 330 miles. How much have you used if you burn 160kgs an hour, if you are travelling at 220mph?

    You travel 220 miles in 1 hour and hence burn 160kg

    Store 160kg, then 330miles - 220miles = 110miles.

    160kg divided by 220 = answer. Take this answer and Multiply by the 110miles = answer. Add 160 to this answer. Think thats right, easier with a pen and paper

    Hope this helps.
     
  4. Re: Speed time distance - your opinion (not so much a how to

    Thanks guys for resisting the urge to mock my mathematical prowess:)

    I think my problem was not breaking it down at the start and instead just panicking because it looked a bit different.

    Still its interesting to see the different ways everybody does these questions.

    Both of your answers were really helpful, thanks a lot for taking the time to explain.

    N.
     
  5. While witsend's way of doing these calculations is correct, bear in mind that (especially on these sort of tests, where they want the numbers to be reasonably easy to work with) there's often an easier way.

    1: Yes, 30 x 45. Or, alternatively, 3*45 then add a 0 on to the end.

    2: I'd do it as: 60 minutes (1 hour) is 3/4 of 80 minutes. Therefore, take 3/4 of 280 to get the answer

    3: Similarly... 330 is 1 and a half times 220, so the time is 1.5 hours. Multiply 1.5 by 160 to get the answer.
     
  6. Thats the simplest explanation I think, I suggest using these methods.
     
  7. Recently passed my FATs (woo!).

    Make sure you know your triangle: S=D/t, t=D/S, D=s*t

    Look for the fraction in everything (especially when given time) E.g. 330 is 3/2*220. So your answer is 160*3/2.

    Know that when you divide a by a fraction you flip the fraction over and multiply e.g.:

    280/(4/3) = 280*3/4.

    Practice lots on http://www.speeddistancetime.info/ - DO IT IN YOUR HEAD!

    (If you haven't seen it yet play a bit on: http://karma.celardore.net/multi/ it is the closest you will find to the CLAN multitasking test although there are quite a few differences)
     
  8. Re: Speed time distance - your opinion (not so much a how to

    At the risk of doing this to death I would make a couple of observations.

    1. All of the advice above is clearly good advice.

    2. I would suggest that although looking for the fractions and, slightly harder, actually spotting them, is of course valid, if you can do the problems this way then you are probably not finding S,T,D difficult in the first place. For this reason witsend's slightly longer explanation which may look more complicated is probably the best approach because it goes back to first principles. The method where you start with so much in so many minutes, divide out to work out how much in 1 minute or 1 hour and then multiply to get however many you want will work every time. I would recommend that you take this methodology.

    3. Learning the triangle is extremely sound advice - draw it out on your working paper at the start for every question if need be. The same applies for any other similar calculations (Ohm's law for budding WEs springs to mind).

    4. And finally, until you get good at the problems, write down every step of your working so that you don't get lost. This should help you break down the problem into manageable chunks and help you get from 'What you know' to 'what you want to know'.
     

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