Two cars left the city for a suburb, 480 km away, at the same time. The speed of one of the cars was 20 km/hour greater than the speed of the other, and that is why it arrived at the suburb 2 hour earlier than the other car. Find the speeds of both cars.

Explanation:

1. Data:

i) Distance traveled by the cars:

ii) Speed of the cars:

iii) Time to arrive at the suburb:

2. Equations:

        time  = distance / speed

               t₂        -       t₁                =  2 hour

               ↓                 ↓                    ↓

           480/v₂    -  480/ (v₂ + 20) =  2

3. Solve the equation

     480(v₂ + 20) - 480(v₂) =  2 × (v₂ + 20) (v₂)

     240(v₂ + 20) - 240(v₂) =  (v₂ + 20) (v₂)

     240v₂ + 4800 - 240v₂ =  (v₂)²  + 20v₂

      (v₂)²  + 20v₂ - 4800 = 0

      (v₂ + 80) (v₂ - 60) = 0

      v₂ = - 80

      v₂ = 60

Only the positive solution has physical meaning:

4.08%

step-by-step explanation:

the answer is 8/21

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