A mobile company manufactured 2000 mobiles in the 5th month and 2750 mobiles in the 8th month. Assuming that the production increases uniformly by a fixed number every month, find the production of mobiles. 1)in the 1st month.
2)in the 10th month. ​

there is only one way to arrange all the eight relative to each other because they are not distinct. we have

now there are nine places to place an (and not more than one in one place).   because we have four symbols, we need to choose four of these nine places to insert an . order does not matter because the are not distinct.

thus there are 1 · c(9,4) ways, or, if we calculate it,

thus there are 126 ways to form such "words."