Shortcut 40:

$$S=\frac DT$$

S = Speed
D = Distance
T = Time taken
Question:
A man travels 200 km in 4 hours. What is the speed in which he travelled?
S = 200/4 = 50 kmph
Question:
A cat runs at a speed of 3 meter per second. How long will it take to cross 3 km?
T = D/S = 3 x 1000 / 3 = 1000 seconds

Shortcut 41:

Relative speed in same direction

$$S_1\sim S_2$$

Question:
Two cars start from same point and travels in same direction at speeds 40kmph and 50kmph. What is the relative speed between them?
Relative speed = 50~ 40 = 10 kmph.

Shortcut 42:

Relative speed in opposite direction

$$S_1+S_2$$

Question:
Two cars start from same point and travels in opposite directions at speeds 40kmph and 50kmph. What is the relative speed between them?
Relative speed = 50 + 40 = 90 kmph.

Shortcut 43:

Time taken to catch a thief

$$T=D/(S_1\sim S_2)$$

Question:
A thief standing 50 away from a police starts running away from him at a speed of 2 m/s. The police suddenly starts chasing him at a speed of 3m/s. How long will the police take to catch the thief?
D = 50m
S1 = 3
S2 = 2
Time taken, T = 50/(3-2)
= 50 seconds

Shortcut 44:
Time taken to meet from opposite direction

$$T=D/(S_1+S_2)$$

Question:
Two persons starts from their home 3km apart and walk towards each other at a speed of 2mps and 3mps. How long (in minutes) will they take to meet each other?