A train is moving on a straight track with speed $20\;ms^{-1}$. It is blowing its whistle at the frequency of $1000\;Hz$ . The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound = $320\;ms^{-1})$ close to :

Question

$\begin{array}{1 1} 12 \% \\ 18 \% \\ 24 \% \\ 6 \% \end{array}$