word problems about algebra

Question

joshua can run four times as fast as william. they start at the same point and run in opposite direction for 40 minutes. the distance between them now is 15 km how fast does joshua run (in km/h)?

Answer 1

Let's william can run at speed : x km/hr

Joshua can run 4 times faster than william so, it is : 4x km/hr

 

They both start at same point so initial distance between them is 0 km.

After 40 minutes distance between them is 15 km.

 

Now 40 minute is 40/60 hr. (Our speed unit is in km/hr so we need everything in hour.)

So in 40/60 hr (or 40 minutes) william can finish x*40/60 Km. (Again Km/hr * hr gives Km)

So Joshua can finish 4x * 40/60 KM.

They are 15 km apart.

So X(40/60) + (4X)(40/60) = 15

(5x)*(40/60) = 15

X(200/60) = 15

X = 15*60/200

x = 4.5 km /hr

 

So Joshua = 4X = 18 km / hr.