In each cell of the arrangement place one of the digits 1,2,3,4,5, so that in each row and each column no digits is repeated. The small number in each region corresponds to the sum or the difference of the two digits place in that region

Scores on a university exam are normally distributed with a mean of 78 and a standard deviation of 8. the professor teaching the class declares that a score of 70 or higher is required for a grade of at least “c.” using the 68-95-99.7 rule, what percentage of students failed to earn a grade of at least “c”?