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    Sorry mods, could you delete please, problem solved! Thanks
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    This is how to tackle the question:

    1.78 m once in 5 attempts

    This means that it was 20% of the time. From a normal distribution table this is 1 - 20% = -80% which = - 0.8416.

    The correct formulae is Z x standard deviation + mean = X

    This means -0.8416 x standard deviation + mean = 1.78

    That is the first part done. Next part:

    1.65m 7 in 10 attemps.

    This means that it was 70% of the time. From a normal distribution table that is 0.52440.

    Substitute this into the correct formulae again.

    This means 0.52440 x standard deviation + mean = 1.65.

    Now you use simultanious equations to work them out. You cancel them, the means cancel out, you can work that out later.

    You now get -1.366x standard deviation = 0.13.

    This means standard deviation is 0.13 divided by -1.366.

    The answer is therefore 0.095.
 
 
 
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