yyxx0412

Calculate teh z-value

Start from choice D: (5%-15%)/10% = -1 (one standard deviation from mean at left side)

                      (25% -15%)/10% = 1 (one standard deviation from mean at right side)

                      therefore teh probability is 68%, which is correct.

                  C: (35%-15%)/10% =2 ( 2 standard deviation from the mean at right side), therefore (1-95%)/2=2.5% which is correct.

Choice B: (5%-15%)/10% = -1, (1-68%)/2 = 16%, 1-16% = 84% , which is correct.

Choice A: (10%-15%)/10% = -0.5, the probability = 30.85% --> A is wrong.