How many different words can be formed by jumbling the letters of the word MISSISSIPPI in which all 'S' come together but all 'I's donot come together 
 

In the word  MISSISSIPPI  there are 4I's ,4 S's, 2P's and M

$\mathrm{Number} \mathrm{of} \mathrm{words} \mathrm{in} \mathrm{which} \mathrm{all} 4 \mathrm{S}\text{'}\mathrm{s} \mathrm{come} \mathrm{together}=\frac{8!}{4!2!}$

$\mathrm{Number} \mathrm{of} \mathrm{words} \mathrm{in} \mathrm{which} \mathrm{all} 4 \mathrm{S}\text{'}\mathrm{s} \mathrm{and} 4 \mathrm{I}\text{'}\mathrm{s} \mathrm{come} \mathrm{together}=\frac{5!}{2!}$

$$\begin{gathered} \mathrm{Number} \mathrm{of} \mathrm{permutations} \mathrm{in} \mathrm{which} \mathrm{all} \mathrm{S}\text{'}\mathrm{s} \mathrm{come} \mathrm{together} \mathrm{and} \\ 4 \mathrm{I}\text{'}\mathrm{s} \mathrm{do} \mathrm{not} \mathrm{come} \mathrm{together}=\frac{8!}{4!2!}-\frac{5!}{2!}=780 \end{gathered}$$