Question

with speed of 80 km/h. it takes 4 hours to cover a certain distance. what should be the speed if the same journey is to be completed in 2 hours.
please answer my question​

Answer 1

$\bold{\underline {\underline {\red{Method\:1}}}}$

$\bold{\underline{\green{Case\:1}}}$

$\bold{Given\::}$

Speed = 80 km/hr.

Time = 4 hrs.

$\bold{Find\::}$

Distance = ?

$\bold{Solution\::}$

Distance = Speed × Time

Substitute the known values in above formula

=> Distance = 80 × 4

=> Distance = 320 km

$\bold{\underline {\green{Case\:2}}}$

$\bold{Given\::}$

Distance = 320 km

Time = 2 hrs.

$\bold{Find\::}$

Speed = ?

$\bold{Solution\::}$

Speed = Distance/Time

Substitute the known values in above formula

=> Speed = 320/2

=> Speed = 160 km/hr.

•°• $\bold{\underline{160\:km/hr.\:is\:the\:speed\:if\:the\:same}}$

$\bold{\underline{journey\:is\:to\:be\:completed\:in\:2\:hrs.}}$

* * *

$\bold{\underline {\underline {\red{Method\:2}}}}$

$\bold{Given\::}$

Speed 1 = 80 km/hr.

Time 1 = 4 hrs.

Time 2 = 2 hrs.

$\bold{Find\::}$

Speed 2

$\bold{Solution\::}$

As said in question distance is same.

So,

S1T1 = S2T2

Substitute the known values in above formula

=> 80 × 4 = S2 × 2

=> 80 × 2 = S2

=> S2 = 160 km/hr.

•°• $\bold{\underline{160\:km/hr.\:is\:the\:speed\:if\:the\:same}}$

$\bold{\underline{journey\:is\:to\:be\:completed\:in\:2\:hrs.}}$