Ishaan has to reach Kolkata which is 737 km away in 21 hours. His starting speed for 7 hours was 49 km/hr. For the next 184 km his speed was 46km/hr. By what speed he must travel now so as to reach Kolkata in decided time of 21hours?

Correct option is D

Given:

Total distance to cover: 737 km

Time limit: 21 hours

Speed for first 7 hours: 49 km/h

Speed for next 184 km: 46 km/h

Formula Used:
Speed =$$\frac{\text{ Distance }}{\text{ Time}}$$​​

Solution:

Distance traveled in first 7 hours = Speed × Time = 49 km/h × 7 hours = 343 km

Distance left after first 7 hours = 737 km - 343 km = 394 km

Time taken to cover 184 km at 46 km/h = $$\frac{\text{184 km }}{\text{ 46 km/h }}$$​= 4 hours

Time left after covering 343 km and 184 km = 21 hours - 7 hours (initial) - 4 hours (next part) = 10 hours

Distance left to cover = 394 km - 184 km = 210 km

Required speed to cover the remaining distance in the remaining time =$$\frac{\text{210 km }}{\text{ 10 hours }}$$​= 21 km/h.