Number of combinations with repetition allowed for JEE

Formula

\[{}^{n+r-1}C_r=\frac{(n+r-1)!}{r!(n-1)!}\]

Variables: \(n\) is number of distinct types, \(r\) is number of selections.

Conditions: \(n\ge 1, r\ge 0\); repetition allowed; order not important.

Selection of items where repeats are allowed, stars and bars basic form.