急 ! F5 about Dispersion 13q2

9) The standard score of Linda in aMathematics test is 1.0. Given that the marks obtained by the students in thistest are normally distributed. Find the percentage of students whose marks arelower than Linda.

P(Z<1)= 0.841345 [By using Excel function normsdist(1)]
The percentage of students whose marks are lower than Linda is 84.1345% 11) The lengths of 6000 metal rods producedby a machine are normally distributed. The mean length and the standarddeviation of the lengths of the rods are 25cm and 0.1cm respectively. If thelength of a metal rod deviates not greater than two standard deviations fromthe mean length, then this metal rod is said to be ‘usable’. Find the number of‘usable’ metal rods with length greater than 25cm.

P(0<Z<2)=0.47725 [By using Excel function normsdist(2)-normsdist(0)]
the number of usable metal rods with length >25 cm
=0.47725*6000 = 2,863.5 [~2864]