1. The problem statement, all variables and given/known data The combination of n different object, taken r at a time(repeatation allowed) is given by Cnr = (n-1+r)! / [(n-1)! r!] 2. Relevant equations 3. The attempt at a solution The above formula is deducted, as it is same as no. of ways of placing n-1 bar in n-1+r places, which is same as combination (repeatation not allowed) of n-1 object placed in n-1+r places. But permutation and combination formula or online calculator doesn't allow when r>n, (r= place, n= no. of objects). Then how is the prove of the above formula deducted? Also the above formula is similar to combination(repeatation not allowed) of n-1+r object placed in r places.