N at a speed of 20km/h reaches his office 10 mins late. Next time he increases his speed by 5km/hr, but is still late by 4 mins. What is the distance of office from his house? :/
x/20 - x/25 = 6/60
because x is distance 20 and 25 are two speeds given and since the time difference is 6 min (10-4) so 6/60 in minutes
rest you can solve yourself :)
By increasing his speed by 25%, he will reduce his time by 20%. (This corresponds to a 6 minutes drop in his time.) Hence, his time originally must have been 30 minutes. Thus required distance = 20 kmph * 0.5 hours = 10 km.