Step-by-step explanation:
The momentum of an object is given by :
............(1)
m is the mas of the object
v is the speed of the object
According to question, arrow's mass is doubled and the speed is halved. So,
m' = 2m
v' = v/2
The new momentum becomes :

p' = mv
p' = p
So, the momentum remains the same. The momentum is changed by a factor of 1. Hence, this is the required solution.