Question 1197053
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Hi  
Recommend the use of a calculator and understanding of the  standard normal curve 

Normal Distribution:  µ = 0 and σ = 1
z score represents the area under the curve to the LEFT of its value
{{{drawing(400,200,-5,5,-.5,1.5, graph(400,200,-5,5,-.5,1.5, exp(-x^2/2)), green(line(1,0,1,exp(-1^2/2)),line(-1,0,-1,exp(-1^2/2))),green(line(2,0,2,exp(-2^2/2)),line(-2,0,-2,exp(-2^2/2))),green(line(3,0,3,exp(-3^2/2)),line(-3,0,-3,exp(-3^2/2))),green(line( 0,0, 0,exp(0^2/2))),locate(4.8,-.01,z),locate(4.8,.2,z))}}}
Using TI or similarly an inexpensive calculator like an Casio fx-115 ES plus
Calculator function Invnorm(X) gives value to the LEFT of z
Middle 60%    |z= Invnorm(20%) = -.84 (to 2 decimal places)
Middle 60%:   -.84 to .84
|{{{blue(16)*(-.84) + 315 = blue (314.46)}}} 
|{{{blue(16)*.84 + 315 = blue (328.44)}}} 
weight from:  314.46 to 328.44

Highest 80 percent:  weight > 314.46


Lowest 15 percent:   |z= Invnorm(15%) = -1.04  |{{{blue(16)*(-1.04) + 315 = blue (298.36)}}}  weight ≤ 298.36
  
Wish You the Best in your Studies.
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