Standard deviation

Question

A tile company produces floor tiles that has an average thickness of 55mm, with a standard deviation of 0.6mm. For premium quality floors, the tiles must have a thickness between 54mm and 55mm. What percent, to the nearest whole number, of the total production can be sold for premium quality floors? 

Answer 1

Obtain a z-chart

http://www.stat.ufl.edu/~athienit/Tables/Ztable.pdf

z = (54 - 55) / 0.6

z = -1 / 0.6

z = -1.6666....

48.56% lie below

50% - 48.56% = 1.44%