If the tension in a stretched string fixed at both ends is changed by 21%, the fundamental frequency is found to increase by 15 Hz then the

f∝T          f2f1=T2T1=1.21T1T1⇒ f1+15f1=1.1⇒f1=150Hz           v2v1=T2T1=1.1⇒v2=1.1v1So velocity increases by 10%. Fundamental wavelength is λ=2L, which remains same as the length of string remains same.