Question

Ganesh covers the distance from P to Q at a uniform speed of 120 kmph and the distance from Q to R at a speed of 80 kmph. What is the average speed for the entire journey if the ratio of the distance PQ and QR is 3:2 ?

Answer 1

The average speed is 100 kmph.

Step-by-step explanation:

Let's assume Ganesh travels the distance PQ in time$T_1$and QR in time $T_2$

• Let the distance PQ be 3x and QR be 2x.

We know that;

• time =$\dfrac{distance}{speed}$

• $T_1 = \dfrac{3x}{120}$  ........(1)

• $T_2 = \dfrac{2x}{80}$  ........(2)

• By solving (1) & (2), we get.

• $T_1 = \dfrac{x}{40}$

• $T_2 = \dfrac{x}{40}$

• $T_1 = T_2$

Also, we know that,

• Average speed = $\dfrac{Total\ Distance}{total\ time}$

• Average speed = $\dfrac{3x + 2x}{T_1 + T_2}$

• Average speed =$\dfrac{3x + 2x}{\dfrac{2x}{40}}$

• Average speed = $\dfrac{5x}{\dfrac{x}{20}}$

• Average speed = 100 kmph