A car starts running at an initial speed of 60 km/h, with its speed increasing every hour by 10 km/h. How many hours will it take to cover a distance of 1210 km?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 11.
Initial speed (a) = 60 km/h
Speed increases (d) = 10 km/h every hour
Total distance to cover (Sn) = 1210 km
Number of hours = n
Sₙ = (n/2)[2a + (n - 1)d]
⇒ 1210 = (n/2)[120 + (n - 1)10]
⇒ 1210 = n(55 + 5n)
⇒ n2 + 11n - 242 = 0
⇒ (n + 22)(n - 11) = 0
⇒ n = 11 hours