I already answered this, both with this misspelling as well as the
correct spelling.
Assuming that you really meant
this misspelling "MISSISIPI", the 3 things
M,SSS,P
can be arranged in 3! = 6 ways:
M SSS P
M P SSS
SSS M P
SSS P M
P M SSS
P SSS M
Then the 4 I's can be placed only 1 way in each of
those so that no I's come together:
IMISSSIPI
IMIPISSSI
ISSSIMIPI
ISSSIPIMI
IPIMISSSI
IPISSSIMI
Answer: 3!*1 = 6
Edwin