Scores on an exam are normally distributed with a mean of 76 and a standard deviation of 10. in a group of 230 tests, how many students score below 66?

Z score = 66 - 76
                 = - 1
                   10 

from the tables of normal distribution  this corresponds to 0.34-3 of the area under the normal curve 
so reuired number od students = 0.3413 * 230  = 78