Aftab's home is situated 120 km from his working place. One day, he was late for office by 2 hours, so he increased the speed of his vehicle by 5 km/hr and thus reached the office on time. What was the speed of Aftab's vehicle on that day?

Let the usual speed of the vehicle be v km/hr, which makes the usual time 120 / v hours. On that day, the speed is (v + 5) km/hr and the time taken is 120 / (v + 5) hours. Since he was originally 2 hours late but reached on time by increasing his speed, we write 120 / v - 120 / (v + 5) = 2. Factoring and solving the resulting quadratic equation (v + 20)(v - 15) = 0 gives the usual speed v = 15 km/hr, so the speed on that day was 15 + 5 = 20 km/hr.

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