Solving for frequency deviation, $\Delta f $ (FM modulation) I'm sorry if I posted this in the wrong section. I solved the question and got $50\textrm{kHz}$, but the solution says it is $100\textrm{kHz}$ without any proof.

Im asking for someone to tell me which is correct.
If you use the standard definition of frequency deviation as the


  "maximum instantaneous difference between an FM modulated frequency and the nominal carrier frequency"


then for the given example you indeed have $\Delta f=50\;\text{kHz}$, because the nominal carrier frequency is $f_c=10\;\text{MHz}$, the maximum frequency is $f_c+\Delta f=10.05\;\text{MHz}$, and the minimum frequency is $f_c-\Delta f=9.95\;\text{MHz}$.