Algebra problem

Question

There are a total of 256 teams in a 3 on 3 basketball tournament.half of the teams are eliminated after each round. After which round would there only be 2 teams left

Answer 1

round 1 128 teams left

round 2 64

round 3 32

round 4 16

5 - 8

6 - 4

7 - 2, after 7 rounds 2 teams are left

it's a GP with r= 1/2= common ratio, a1 = 256 = 1st term

2 = an = a1r^(n) solve for n

2/256 = .5^(n)

1/128 = (1/2)^(n)

n = 7 as 1/2^7 = 1/128