Question 1174438
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Hi
  Normal Distribution:  μ = 48m  and   σ = 7mos 
manufacturer does not want to exchange more than 10% of the watches
{{{z =blue (x - mu)/blue(sigma)}}}
  z = 1.282 represents 10% of the Standard Normal Curve
  
 {{{1.282 = blue (x - 48)/blue(7)}}}
    x = 7(1.282) + 48 = 56.97 (rounding down to 56)  
90% are expected to have lifetime of 56mo
 For how many months should a guarantee be made:  56mo
Wish You the Best in your Studies.
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