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Math Help - normal approximation?

  1. #1
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    normal approximation?

    From past data, it is known that 70perent of brand A computer users plan to buy a newer model of brand A computer in the future. Suppose 25 brand A customer users are interviewed for their future preference. Use normal approximation to find

    1) the chance that more than 10 of these users intend to switch brand in the next computer purchase
    2) the chance that exactly 10 of these user intend to switc brand in their next purchase.

    the answer is 0.1922 and 0.096 please show reasoning
    Can binomial be used in this?
    Isn't the p here 0.3 and n = 25
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  2. #2
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    Quote Originally Posted by sankeel View Post
    Can binomial be used in this?
    Isn't the p here 0.3 and n = 25
    Yes it could. But if you need to use binomial approximation to the normal you should ask yourself is n=25 a good sample size?

    If you go that way \mu = n\times p , \sigma = \sqrt{n\times p \times (1-p)}
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