If the frequency of a wave is increased by 25%, then the change in its wavelength will be: (medium not changed)

Since, the medium has not changed, speed of wave remains same.⇒v = fλ = constantf1λ1 = f2λ2⇒ f1λ1 = (1.25f1)λ2    (∵ frequency increased by 25%)λ2 = λ11.25  ⇒λ2 decreases.% change in wavelength = λ1-λ2λ1×100λ1-λ11.25λ1×100 = 0.251.25×100 = 1005 = 20%