8. The scores in an exam are Normally distributed with mean 59. 95% of the students had their grades between 49 and 69. Based on 68-95-99.7 rule, what must be the standard deviation of the scores? (a) n - 59 D 5 69: 59 - 2047 49= 59-2(*) 69- 59 =-LX (C) 3.33 49- 59 = -2(*) 10 =-2 x 20 - 10 = 2( ) - 2 S =x -5: * None of the above gives the correct answer based on 68-95-99.7 rule