Question

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?

Answer 1

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