140k views
1 vote
A motorist travels for 20km at one speed, and then increased her speed by 20 kph

for next 30 km. How fast was she traveling originally if the total trip took 1 hour?

1 Answer

2 votes

Answer:

The original speed was 40 kph which increased to 60 kph

Explanation:

r * t + (r + 20)*(1 - t) = 50

r * t + (r - rt + 20 - 20*t = 50

r + 20 - 20t = 50

20/r + 30/(r + 20) = 1

20(r + 20) + 30*r = r(r + 20)

20*r + 400 + 30r = r^2 + 20r

r^2+20r = 20*r + 30r + 400

r^2 - 30r - 400 =0

(r - 40)(r + 10) = 0

r = 40 kph is the only root that works. r = - 10 has no meaning in this kind of question at all

User Andy Hayden
by
7.2k points
Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.