Answer:
The speed doubles.
Explanation:
The speed of a wave in a string is:
v = √(T / ρ)
where T is the tension and ρ is the linear density (mass per length).
If T is held constant, and ρ decreases by 1/4, then:
v = √(T / (ρ/4))
v = √(4T / ρ)
v = 2√(T / ρ)
The speed doubles.
