Question

A man covers first 70 km of a journey at 35km/hr and the remaining 40km at 10 km/hr.Find the average speed of the whole journey

Answer 1

first time (t1) = distance/speed
=70/35=2 hours
second time (t2)= 40/10
= 4 hours
average speed = total distance / total time
= 70 + 40 / 2+4
= 1.8 km/hr

Answer 2

${ \bf{ \underline{ \red{\underline{ \red{Solution : - } }}}}}$

{ Accirding to question }

Case 1 :- Distance covered by man with speed is as follow,

Distance = 70 km & Speed = 35 km/hr

Case 2 :- Distance covered by man with speed is as follow,

Distance = 40 km & Speed = 10 km/hr

Now we need to find time for case 1 we use formula

${ \bf{ \dashrightarrow{Speed = \frac{ Distance }{Time} }}}$

${ \bf{ \dashrightarrow{35 = \frac{ 70 }{Time} }}}$

${ \bf{ \dashrightarrow{Time = \frac{ 70 }{35} }}}$

${ \bf{ \dashrightarrow{Time = 2 \: hour}}}$

2 hour taken by person to cover 70 km with speed 35 km/hr.

Now we need to find time for case 2 we use formula

${ \bf{ \dashrightarrow{Speed = \frac{ Distance }{Time} }}}$

${ \bf{ \dashrightarrow{10 = \frac{ 40 }{Time} }}}$

${ \bf{ \dashrightarrow{Time = \frac{ 40 }{10} }}}$

${ \bf{ \dashrightarrow{Time = 4 \: hour }}}$

4 hour taken by person to cover 40 km with speed 10 km/hr.

Now, to calculate average speed

${ \bf{ \small {\dashrightarrow{Average \: speed = \frac{ Total \: distance }{Total \: time} }}}}$

${ \bf{ \small {\dashrightarrow{Average \: speed = \frac{70 + 40}{2 + 4} }}}}$

${ \bf{ \small {\dashrightarrow{Average \: speed = \frac{110}{6} }}}}$

${ \bf{ \small {\dashrightarrow{Average \: speed = 18.33 \:km/hr }}}}$

Hence average speed of the whole journey is 18.33 km/hr.