sir how to solve time and work give me tips and tricks

• In a journey travelled with different speeds, if the distance covered in each stage is constant, the average speed is the harmonic mean of the different speeds.
• In a journey travelled with different speeds, if the time travelled in each stage is constant, the average speed is the arithmetic mean of the different speeds.
While converting the speed in m/s to km/hr, multiply it by 3.6. It is because 1 m/s = 3.6 km/hr. Hence, 5 m/s = 5*3.6 km/hr = 18 km/hr
• Distance = Speed * Time
• Speed = Distance / Time
• Time = Distance / Speed

Time taken = Total Work / Speed of Doing work

If A and B are moving in opposite directions with speeds x m/s and y m/s respectively, their relative speeds with respect to each other will be
Relative Velocity = (x+y) m/s

If A and B are moving in the same direction with x m/s and y m/s then A’s relative velocity wrt B is
Relative Velocity = (x-y) m/s and B’s relative velocity wrt A is
Relative Velocity = (y-x) m/s

If the speed of stream is 'W' and speed of a boat in still water is 'B'
• Speed of the boat downstream is B+W
• Speed of the boat upstream is B-W