Question

a train has to move 120 km distance by covering 40 km with a speed of 20km/hr. what should be the speed for remaining distance so that average speed for entire next journy is 40 km/hr.

plz tell tye solution the answer is 60km/hr​

Answer 1

Given :

a train has to move 120 km distance by covering 40 km with a speed of 20km/hr. what should be the speed for remaining distance so that average speed for entire journey is 40 km/hr.

To Find :

Speed for remaining distance ( 80 km )

Solution :

Average speed is defined as total distance travelled per total time

$\bigstar\ \; \sf \pink{A_{Speed}=\dfrac{Total\ distance}{Total\ time}}$

_____________________________________________

Total distance = 120 km

Average speed = 40 km/h

Speed for 40 km = 20 km/h

Remaining distance = 120 - 40 = 80 km

Speed for remaining distance = v

$\to \sf A_{Speed}=\dfrac{120}{t_{40\ km}+t_{80\ km}}$

• Time = Distance / Speed

$\to \sf 40=\dfrac{120}{\frac{40}{20}+\frac{80}{v}}\\\\\to \sf 40=\dfrac{120}{2+\frac{80}{v}}$

$\to \sf 40=\dfrac{120}{\frac{2v+80}{v}}\\\\\to \sf 40=\dfrac{120v}{2v+80}$

$\to \sf 40(2v+80)=120v\\\\\to \sf 80v+3200=120v\\\\\to \sf 120v-80v=3200\\\\\to \sf 40v=3200\\\\\leadsto \sf \blue{v=80\ km/h}\ \; \bigstar$

Answer 2

Explanation:

Given :

a train has to move 120 km distance by covering 40 km with a speed of 20km/hr. what should be the speed for remaining distance so that average speed for entire journey is 40 km/hr.

To Find :

Speed for remaining distance ( 80 km )

Solution :

Average speed is defined as total distance travelled per total time

\bigstar\ \; \sf \pink{A_{Speed}=\dfrac{Total\ distance}{Total\ time}}★ A

Speed

=

Total time

Total distance

_____________________________________________

Total distance = 120 km

Average speed = 40 km/h

Speed for 40 km = 20 km/h

Remaining distance = 120 - 40 = 80 km

Speed for remaining distance = v

\begin{gathered}\to \sf A_{Speed}=\dfrac{120}{t_{40\ km}+t_{80\ km}}\\\\\end{gathered}

→A

Speed

=

t

40 km

+t

80 km

120

Time = Distance / Speed

\begin{gathered}\to \sf 40=\dfrac{120}{\frac{40}{20}+\frac{80}{v}}\\\\\to \sf 40=\dfrac{120}{2+\frac{80}{v}}\end{gathered}

→40=

20

40

+

v

80

120

→40=

2+

v

80

120

\begin{gathered}\to \sf 40=\dfrac{120}{\frac{2v+80}{v}}\\\\\to \sf 40=\dfrac{120v}{2v+80}\end{gathered}

→40=

v

2v+80

120

→40=

2v+80

120v

\begin{gathered}\to \sf 40(2v+80)=120v\\\\\to \sf 80v+3200=120v\\\\\to \sf 120v-80v=3200\\\\\to \sf 40v=3200\\\\\leadsto \sf \blue{v=80\ km/h}\ \; \bigstar\end{gathered}

→40(2v+80)=120v

→80v+3200=120v

→120v−80v=3200

→40v=3200

⇝v=80 km/h ★