A man while going to the office increases his speed to 6/5 of his actual speed and reaches 1 hour early. Find his actual speed if the distance between his home to office is 30 km.

When speed increases to 6/5 of actual speed, time decreases to 5/6 of actual time (inverse proportion). The time saved is 1 hour, which is 1 - 5/6 = 1/6 of actual time. So actual time = 6 hours. With distance 30 km and time 6 hours, actual speed = 30/6 = 5 km/hr. At 6/5 speed (6 km/hr), time = 30/6 = 5 hours, saving 1 hour as given.