Speed Distance Time

Discussion in 'Join the Army - Regular Officer Recruiting' started by chrismalaga, Oct 18, 2011.

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  1. Hello All,

    Now I know that this had probably been done to death already but I am really struggling with these so I could do with the help. My first question is: do you have to do Speed Distance Time from the top of your head at the AOSB or can you use a pen and paper like they can at RAF selection? 2. Does anyone have any easy to understand techniques for how to do the hard ones mentally?

    Thanks for all your advice in advance.

    Chris Emms
  2. Brotherton Lad

    Brotherton Lad LE Reviewer

    Can you stick an example up? Sounds like simple mental arithmetic to me.
  3. Chris try to remember this T= Time S= Speed D = Distance

    Draw a triangle with a line through the middle - at the top place a T for time - underneath place a s for speed and a D for distance

    you now have a formulea for working it out - eg

    T = speed x distance
    D = time divided by speed

    get the general idea
  4. Or, if you want to get the right answer, try putting D at the top and S & T at the bottom.

    BBC - Standard Grade Bitesize Maths I - Distance, speed and time
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  5. Brotherton Lad

    Brotherton Lad LE Reviewer

    If that's all it is (don't know about modern triangle methods, though I see where you're going), then, and being all up to date and metric:

    Think - using 60 kph over 2 hours as an example

    Speed in kph eg 60 = 120/2 or S = D/T

    So Distance = kph x time eg 120 = 60 x 2 or D = S x T

    And Time = distance/kph eg 2 = 120/60 or T = D/S

    Look at the question, don't do any maths to start with, just think if you were walking or driving; how long? how far? how quick? Get a rough idea, then do the maths.

    (I do despair slightly, isn't this what you do before going to big school or have calculators and computers removed the requirement?)
  6. Modern triangle methods? GG, I left school in 1965 (yeah, yeah, paper had been invented then) and we were always taught that way for formulae. Just like P=IxE (P on top, I and E on the bottom - stick your finger over the one you want to find so E = P/I)
    Must have been rediscovered.
  7. You have to do them in your head during an interview but you can use paper during the planex
  8. If you remember that in an equation "per" means "divide by" then remembering "speed = miles per hour" should be all you need to memorise, assuming, you can remember how to do very basic maths.

    Best way to get in practice with this sort of thing is to just do calculations in your head all the time with numbers you see, eg: on car number plates, speed limit signs, petrol station prices etc.
    • Like Like x 1
  9. 6 minute rule.

    At x mph you'll cover x/10 miles every 6 minutes and 1/2 of x/10 every 3.

    So at 80 mph you'll cover 8 miles every 6 minutes, 12miles every 9 minutes, 16 miles every 12 minutes and so on it's a good ready reckoner

    How far will you travel in 12 minutes at 90 mph? becomes an instant 18 miles in your head as opposed to trying to do the calculation and getting the units right. Obviously it works for Km/h too but answer is in km.
    • Like Like x 1
  10. Brotherton Lad

    Brotherton Lad LE Reviewer

    Must have been. Not seen till today for me, I think. I actually can't remember how I was taught to invert equations, though I do recall learning the 12 times tables by rote at the age of 5 (just before you left school).
    • Like Like x 1
  11. RJM

    RJM Swinger

    just remember 1 and algerbraicly re-arrange. s=d/t is the one I remember and then it can be re-arranged easily enough:

    s=d/t Multiply both sides by t to give
    st=d this is your equation where d is the subject. Finally divide by s
    t=d/s for your equation where t is the subject.
  12. In your interview you will have to do one off the top of your head. Everybody recommends that when you do this you should speak your thinking out loud so that the interviewer can at least see that you haven't just frozen up.

    You have probably already seen this link but, just in case you haven't, I'll put it up because it is indispensable: Speed Distance Time | OASC: RAF Officer and Aircrew Selection Centre

    Read the advice on that page (the one in the link) carefully.

    Learn the divisions of an hour:

    2 of 30 minutes 1/2 hour = 30 mins
    3 of 20 minutes 1/3 hour = 20 mins, 2/3 hour = 60 mins
    4 of 15 minutes 1/4 hour = 15 mins, 3/4 hour = 45 mins
    5 of 12 minutes 1/5 hour = 12 mins, 2/5 hour = 24 mins, 3/5 hour 36 mins, 4/5 hour = 48 mins
    6 of 10 minutes 1/6 hour = 10 mins, 2/6 hour = 20 mins...
    10 of 6 minutes 1/10 = 6 mins
    12 of 5 minutes 1/12 = 5 mins
    15 of 4 minutes 1/15 = 4 mins
    20 of 3 minutes 1/20 = 3 mins
    30 of 2 minutes 1/30 = 2 mins

    These quickly become second nature, so when presented with a Speed question like:
    "What speed covers 6 miles in 24 mins?"
    You already know that 24 mins is 2/5 of an hour. Therefore 6 miles is 2/5 of the speed
    (You covered 6 miles in 2/5 of an hour, so your speed is 6 miles per 2/5 of an hour).
    So work out what it is for 5/5 of an hour:
    6 = 2/5 of an hour
    3 = 1/5 of an hour
    15 = 5/5 of an hour ---> 15 miles per hour

    Here's a slightly bigger example:

    "What speed covers 288 miles in 9 hours and 36 mins?"
    The "36 mins" is the key clue. 36 mins is 3/5 of an hour, so you know you're working in fifths of hours.
    36 mins = 3/5 of an hour
    9 hours and 36 mins = 48/5 of an hour
    Therefore, 288 miles = 48/5 of the speed per an hour
    .... work out what 1/5 is....so that you can work out what 5/5 is:
    288 = 48/5
    (48,96,144,192,240,288.........288 divided by 48 = 6)
    6 = 1/5
    30 = 5/5..... 30 miles per 5/5 of an hour....30mph

    Do the automated tests over and over and over...

    You'll start to get good at the little ones and develop your own quick, logical way of doing them.

    For the tricky, bigger ones:
    Stop muddling yourself up trying to work it out.
    Clear your mind.
    Go back to the basic S=D/T , T= D/S , D=SxT
    Write it all out (in the plan-ex)
    Say it out loud (in the interview)
  13. Well in the world of the fps system of units another relationship useful to remember is that 88 feet per second equates to 60 miles per hour .
  14. What's a foot?
  15. something is afoot with Princess Productions .... well according to ARRSE .