Question

a person travelled from bangalore to chennai and found his average speed to be 60 km/hr. for the return journey to bangalore he travelled at night and found average speed to be 90km/hr. what is the average speed for the complete round trip?

Answer 1

a person travelled from Banglore to Chennai and found his average speed to be 60 km/h
Let $V_1=60km/h$

for the return journey from Chennai to Banglore , he travelled at night and found his average speed to be 90 km/h
Let $V_2=90km/h$

use the formula,
$V_{average}=\frac{2V_1V_2}{V_1+V_2}\\\\=\frac{2\times60\times90}{60+90}\\\\=\frac{120\times90}{150}=72km/h$

hence, average speed for the complete round trip is 72 km/h

Answer 2

$\bf{hey}$
$\underline{here \: is \: the \: answer}$
⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇

$\bf{v} \tiny{1}$
$\bf{ = 60km \: per \: hour}$

$\bf{v} \tiny{2}$
$\bf{ = 90km \: per \: hour}$

⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐

____________________________________

$\bf \huge{v} \tiny{average} \huge = \frac{2v \tiny{1} \huge{v} \tiny{2}}{v \tiny{1} \huge{ + v} \tiny{2}}$

hence,

▶2×60×90/60+90

▶120×90/150

▶10800/150

▶72 km/hr

$\bf{hence \: answer \: is \: 72km/ hr}$

$\huge{hope \: it \: helps}$

$\huge{thanks}$