A man in a train notices that he can count 41 telephone posts in one minute. If they are known to be 50 metres apart, then at what speed is the train travelling?

Answer: Option B

Explanation:

Time taken to cover 600 km = 6 hours [because train speed is 100 km/hr]

Number of stops =
begin{aligned}
frac{600}{75} - 1 = 7 \
text{Total time on stops =}7*3 = 21 mins

end{aligned}
Total time taken by train = 6 hours 21 mins

Answer: Option B

Explanation:

$$\begin{aligned} Speed = \left(80*\frac{5}{18}\right) m/sec \\ = \frac{200}{9} m/sec \\ = 22\frac{2}{9} m\sec \end{aligned}$$

Answer: Option A

Explanation:

Let the distance be 3x km,
then,
$$\begin{aligned} \frac{x}{3} +\frac{x}{4} +\frac{x}{5} = \frac{47}{60} \\ \frac{47x}{60} =\frac{47}{60} \\ x = 1 \end{aligned}$$
So total distance = 3*1 = 3 Km

Answer: Option D

Explanation:

$$\begin{aligned} Speed = \frac{Distance}{Time} \\ = \frac{200}{24}m/sec = \frac{25}{3} m/sec \\ \frac{25}{3}*\frac{18}{5} km/hr = 30 km/hr \end{aligned}$$

Answer: Option D

Explanation:

We need to calculate the distance, then we can calculate the time and finally our answer.
Lets solve this,

Let the distance travelled by x km
Time = Distance/Speed

$$\begin{aligned} \frac{x}{10} - \frac{x}{15} = 2 \\ \text{[because, 2 pm - 12 noon = 2 hours]} \\ 3x - 2x = 60 \\ x = 60. Time = \frac{Distance}{Speed} \\ Time @ 10km/hr = \frac{60}{10} = 6 hours \end{aligned}$$
So 2 P.M. - 6 = 8 A.M
Robert starts at 8 A.M.

He have to reach at 1 P.M. i.e, in 5 hours

So, Speed = 60/5 = 12 km/hr