Question

Atul took a non-stop flight to visit his grandmother. The 1200km took three hours and 45 minutes because of bad weather, the return trip took four hours and 45 minutes what was his average speed for the round trip?​

Answer 1

Given :-

Distance (D) =1200km

$\sf Time (T_1)= 3h \ 45 min \\ \\ \sf Time (T_2)= 4 h \ 45 min$

To find :-

Average speed of whole trip

• Now ,

Average speed :- It is defined as the total distance covered by a body divided by total time taken

$\boxed{\sf{\dag \ \ Average \ speed = \dfrac{Total \ distance }{Time \ Time }}}$

• In the whole trip the distance remains same !

$\implies\sf D_1= 1200km \\ \\ \implies\sf D_2= 1200km\\ \\ \implies\sf T_1= 3+\cancel{\dfrac{45}{60}}\\ \\ \implies\sf T_1= 3+0.75 =3.75\ hours \\ \\ \implies\sf T_2= 4+\cancel{\dfrac{45}{60}} \\ \\ \implies\sf T_2= 4+0.75= 4.75\ hours$

• Now find the average speed

$\longmapsto\sf Average\ speed =\dfrac{D_1+D_2}{T_1+T_2}\\ \\ \longmapsto\sf Average\ speed = \dfrac{1200+1200}{3.75+4.75}\\ \\ \longmapsto\sf Average\ speed = \cancel{\dfrac{2400}{8.5}}\\ \\ \longmapsto\sf Average \ speed = 282.35km/h$

$\therefore{\underline{\textsf{\textbf{Average\ speed \ of \ whole \ trip = 282.35km/h}}}}$

Answer 2

Given

⟡ Distance b/w Atul's house & grandmother's house = 1200 km.

⟡ Time to go there = 3 hours & 45 minutes.

⟡ Time to return = 4 hours & 45 minutes.

To find

◆ Average speed of whole trip.

Solution

Here, as he goes & comes back meaning that he crossed same distance twice.

So, distance 1 = 1200 km

Distance 2 = 1200 km.

Again, time of 1st trip = 3 h & 45 mins.

→ Time of 1st trip = 3 + (45/60) = 3.75 h

Time for 2nd trip = 4 h & 45 mins.

→ Time of 2nd trip = 4 + (45/60) = 4.75 h

We know that,

$\longmapsto\underline{\boxed{\sf\blue{Average \: speed = \dfrac{Total \: distance}{Total \: time} }}}\\\\\longmapsto\sf Av. speed = \dfrac{d_1 + d_2}{t_1 + t_2}\\\\\longmapsto\sf Av. speed = \dfrac{1200 + 1200}{3.75 + 4.75}\\\\\longmapsto\sf Av. speed = \dfrac{2400}{8.5} \\\\\longmapsto\underline{\boxed{\textsf{\textbf{Av. speed = 282.35 km/h }}}}\\\\\\\therefore\underline{\textsf{Average speed of whole trip = {\textbf{282.35 kmh ^{\text{-1}} }}}}$