Section 3.1 question about "correct value is halfway between... extremes"

[ghjwp7]

Third paragraph from end of 3.1 says in part "there are 2ⁿ possible values for a key" with between 1 and 2ⁿ guesses needed, and "the average number of guesses to discover the correct value is halfway between those extremes" which it shows as 2^(n/2) rather than as 2ⁿ/2 or 2^(n-1)

url = https://security.systemsapproach.org/crypto.html

(However, calculation in 3.2 is ok: "half of the space of 2^56 possible keys ... giving 2^55 ... keys")