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# S1 question help - solved Watch

1. Sorry mods, could you delete please, problem solved! Thanks
2. 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.

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Updated: December 22, 2010
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