A car starts running with an initial speed of 50 km/hour, with its speed increasing every hour by 5 km/hour. How many hours will it take to cover a distance of 630 km?

A7 hours

B9 hours ✓ Correct

C6 hours

D8 hours

Correct answer: (B) 9 hours

Explanation

The car needs 9 hours to cover 630 km.

Hourly distances form an AP: 50, 55, 60, ... increasing by 5.

Sum of n hours = n/2 x (2 x 50 + (n - 1) x 5) = 630.

This gives n^2 + 19n - 252 = 0.

Solving, n = 9.

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