Move to one end of the list and press C-@ (or C-SPC or whatever) to set the mark, then move to the other end of the list and type M-# g.
1: [2.3, 6, 22, 15.1, 7, 15, 14, 7.5, 2.5]
.
To make things interesting, let's assume we don't know at a glance how many numbers are in this list. Then we could type:
2: [2.3, 6, 22, ... ] 2: [2.3, 6, 22, ... ]
1: [2.3, 6, 22, ... ] 1: 126356422.5
. .
RET V R *
2: 126356422.5 2: 126356422.5 1: 7.94652913734
1: [2.3, 6, 22, ... ] 1: 9 .
. .
TAB v l I ^
(The I ^ command computes the nth root of a number. You could also type & ^ to take the reciprocal of 9 and then raise the number to that power.)