810
The coefficient of \(xy^2z^3\) in the polynomial expansion of \((x - 2y + 3z)^6\) is determined by identifying the term that matches the desired variables and their exponents. This is achieved through the multinomial expansion, where the specific term we are interested in is given by: \[ \binom{6}{1, 2, 3} \cdot 1^1 \cdot (-2)^2 \cdot 3^3 = \frac{6!}{1! \cdot 2! \cdot 3!} \cdot 1 \cdot 4 \cdot 27 = 60 \cdot 4 \cdot 27 = 6480 \] Thus, the coefficient is 6480.
The number of 6-letter words, with or without meaning, that can be formed using the letters of the word MATHS such that any letter that appears in the word must appear at least twice, is $ 4 \_\_\_\_\_$.
