# Creating Strings: Number of Strings Number of ways of arranging \( n \) items: \( n!. \) Number of arranging \( m_1 \) identical items, \( m_2 \) identical items, \( \dots \), \( m_l \) identical items: \[ \frac{(m_1 + m_2 + \dots m_l)!}{m_1! \, m_2! \, \dots \, m_l!}. \] Example: Number of different strings we can create out of the letters in the string "aabac": \[ \frac{(3 + 1 + 1)!}{3! \, 1! \, 1!} = \frac{5!}{3!} = 20. \]