You can think of it finding the total area from z=-1.74 and the additional area from z=-1.02 , thus now you need to subtract them.Originally Posted bywild_flowr69

Looking up at the tables, http://www.isixsigma.com/library/con...stribution.asp

For z=-1.74 we get 0.4591 and for z=-1.02 we get 0.3461

Thus, the difference is .113

That is 11.3%