In Young's double slit experiment how many maximas can be obtained on a screen (including the central maximum) on both sides of the central fringe if  $\lambda =2000\AA$ and  $d=7000\AA$

For maximum intensity on the screen
$$\begin{gathered} d\sin \theta =n\lambda \\ \Rightarrow \sin \theta =\frac{n\lambda }{d}=\frac{n\left(2000\right)}{7000}=\frac{n}{3.5} \end{gathered}$$
Since maximum value of  $\sin \theta$ is 1
So $n=0,1,2,3,$  only. Thus only seven maximas can be obtained on both sides of the screen.