Correct Answer - Option 2 : 30
Calculation:
Total distance between A and B = 800 km
(i) Speed for first 50% distance (400 km) = 10 km/hr
(ii) Speed for next 1/4th of the remaining distance (400/4 = 100 km) = 20 km/hr
(iii)Speed for the remaining distance (300 km) = s km/hr
Average Speed = (Total Distance)/ (Total Time)
Total Time = (400/10) + (100/20) + (300/s)
⇒ (40 + 5 + 300/s)
⇒ (45 + 300/s)
∴ Average Speed = 800/ (45 + 300/s)
⇒ 14(6/11) = 800/ (45 + 300/s)
⇒ 160/11 = 800/ (45 + 300/s)
⇒ 160/11 = 800s/ (45s + 300)
⇒ 1/11 = 5s/ (45s + 300)
⇒ 45s + 300 = 55s
⇒ (55s – 45s) = 300
⇒ 10s = 300
⇒ s = 300/10
⇒ s = 30 km/hr
∴ The value of s is 30 km/hr.