Answer:
The original speed was 40 kph which increased to 60 kph
Step-by-step 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
