A person climbs up a stalled escalator in 60 s. If standing on the same but escalator running with constant velocity he takes 40 s. How much time is taken by the person to walk up the moving escalator?
(1) 37 s
(2) 27 s
(3) 24 s
(4) 45 s

A horse rider covers half the distance with $5 \mathrm{~m~s}^{-1}$ speed. The remaining part of the distance was travelled with speed $10 \mathrm{~m~s}^{-1}$ for half the time and with speed $15 \mathrm{~m~s}^{-1}$ for other half of the time. The mean speed of the rider averaged over the whole time of motion is $\frac{x}{7} \mathrm{~m~s}^{-1}$. The value of $x$ is $\_\_\_\_$.

A particle moving in a straight line covers half the distance with speed $6 \mathrm {~m} / \mathrm { s }$. The other half is covered in two equal time intervals with speeds $9 \mathrm {~m} / \mathrm { s }$ and $15 \mathrm {~m} / \mathrm { s }$ respectively. The average speed of the particle during the motion is :
(1) $10 \mathrm {~m} / \mathrm { s }$
(2) $8 \mathrm {~m} / \mathrm { s }$
(3) $9.2 \mathrm {~m} / \mathrm { s }$
(4) $8.8 \mathrm {~m} / \mathrm { s }$