Question

lamp-posts are placed 30 metresapart along road. How long will a car travelling at 45 km an hour take to pass 6 lamp-post, not counting the first of them.

Answer 1

$$\begin{gathered} Dis\tan ceof{6}^{th}lamppost=30+30+30+30+30+30=180m \\ Speedofacar=45km/h=45\times \frac{1000}{3600}=12.5m/s \\ Inonesecitcovers12.5m \\ Withoutcounting{1}^{st}lamppostdis\tan ce=180-30=150m \\ Timetakentocover6thlamppost=\frac{dis\tan ce}{speed}=\frac{150}{12.5}=12s \end{gathered}$$