The distance between city A and B is 600 km... the entire thing does not fit here, so I have added it to the description.

Question

The distance between city A and B is 600 km. The first train left A and headed towards B at the speed of 60 km/hour. The second train left B three hours after the first train left A, and it traveled with a speed of v km/hour. The trains met t hours after the time at which the first train left A. Express v in terms of t. Find the speed v if t=7; t=6.

Answer 1

 

   →60t                     v(t-3)←

A*---------------------------------*B

                     600km

 

distance = rate(time) or d=rt

 

d_a = 60t      distance travelled from A in t hours

d_b = v(t-3)   distance travelled from B in 3 less than t hours

                   because train B left 3 hours later

 

We need the distances travelled by both to sum to 600km

 

60t + v(t-3) = 600

subtract 60t from both sides

v(t-3) = 600 - 60t

divide both sides by (t-3)

 

v = (600-60t)/(t-3)

 

For t=7:

v = (600-60(7))/(7-3)

  = (600-420)/4

  = 180/4

v = 45 km/hr

 

You try for t=6.

Just plug into the formula as I did above.

Let me know if you have questions or problems.

Cheers.

 

Andrew M.