How many groups of four elements can be formed from nine elements .

There are 9 elements.

Let the
number of ways we can group 4 elements from 9 elements be
x.

The number of different ways can we arrange the 9
different elements in consecutive 4 places  is  9P4 ways = 9*8*7*6
ways.

Alternatively ,  let number of ways of selection of 4
distinct elements from 9 elements be  x . And each group could be arranged in 4!
arrangements within itself. So x different groups of 4 elements could be arranged in
4!*x ways.

Therefore x*4! =
9*8*7*6.

Therefore x =
9*8*7*6/4!.

x =
9*8*7*6/4*3*2*1.

x =
126.

Therefore the number of ways  selecting the   group of
4 elements from 9 elements is 126.