Question

A man covers the first 70 km of his journey at 35 km/h and the remaining 80km at 20 km/h. Find:
1.The total time taken.
2.His average speed during the whole journey.

Answer 1

Step-by-step explanation:

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} }}}⇢Speed=TimeDistance

{ \bf{ \dashrightarrow{35 = \frac{ 70 }{Time} }}}⇢35=Time70

{ \bf{ \dashrightarrow{Time = \frac{ 70 }{35} }}}⇢Time=3570

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

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} }}}⇢Speed=TimeDistance

{ \bf{ \dashrightarrow{10 = \frac{ 40 }{Time} }}}⇢10=Time40

{ \bf{ \dashrightarrow{Time = \frac{ 40 }{10} }}}⇢Time=1040

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

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} }}}}⇢Averagespeed=TotaltimeTotaldistance

{ \bf{ \small {\dashrightarrow{Average \: speed = \frac{70 + 40}{2 + 4} }}}}⇢Averagespeed=2+470+40

{ \bf{ \small {\dashrightarrow{Average \: speed = \frac{110}{6} }}}}⇢Averagespeed=6110

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

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