 Hi and welcome to our session. Let us discuss the following question. The question says how many three digits numbers can be formed by using the digits 1 to 9 if no digit is repeated? In this question we will make use of theorem 1. The theorem 1 states that the number of commutations different objects taken are at a time and the objects do not repeat different objects and r is the number of objects taken at it upon to solve this question with the solution. Using these digits, imitations of n different objects taken are at a time and the object student repeats is n p r is equal to the number of using the digits 1 to 9.