We know the relation
v=nxxlambdav=n×λ
Where
n->"frequency of wave"n→frequency of wave
lambda->"wave length of wave"λ→wave length of wave
v->"velicity of wave"v→velicity of wave
Velocity of wave being constant we can say
n_1xxlambda_1=n_2xxlambda_2.....[1]
Where
n_1->"initial frequency"
lambda_1->"initial wave length"
n_2->"changed frequency"
lambda_2->"changed wave length"
By the given condition the wave length is reduced by 50%.
So
lambda_2=50%xxlambda_1=lambda_1/2
So by relation [1]
n_1xxlambda_1=n_2xxlambda_1/2
=>n_2=2n_1
Percent increase in frqyency
=(n_2-n_1)/n_1xx100%
=(2n_1-n_1)/n_1xx100%=100%