Question

A train leaves little rock Arkansas, travels north at 85 kilometers per hour. another train leaves same time and travels south at 80 kilometers per hour. How long will it take before they are 495 kilometers apart

Answer 1

Hi,

Let us denote first train with T₁, its distance d₁, its speed v₁ = 85 km/h.

Similarly, second train would be with T₂, its distance d₂, its speed v₂ = 80 km/h. Also, let d be total distance, d = 495 km.

Given being the fact that train T₁ travels north, and train T₂ travels south, their path is on a straight vertical line. Please create a simple drawing, you will see the vertical line immediately.

Then, we need to find the time t, when d₁ + d₂ = d = 495 km (1)

Each speed v₁, and v₂ is constant, therefore we apply very well known formula:

d₁ = v₁·t, and d₂ = v₂·t (2).

From (1) and (2) we have:

v₁·t + v₂·t = d, or (v₁ + v₂)t = d ⇒ t = d/(v₁ + v₂) = 495/(80 + 85) = 495/165 = 3 hours.

So, it takes 3 hours to have those 2 trains 495 km apart.

Green eyes.