The task is to generate the correct answer for a given math problem.

Problem: of the seven - digit positive integers that have no digits equal to zero , how many have two digits that are equal to each other and the remaining digit different from the other two ?
152409600

Problem: set a { 3 , 3,3 , 4,5 , 5,5 } has a standard deviation of 1 . what will the standard deviation be if every number in the set is multiplied by 8 ?
d ) 8

Problem: a student travels from his house to school at 10 km / hr and reaches school 2 hours late . the next day he travels 15 km / hr and reaches school 1 hour early . what is the distance between his house and the school ?

90