arithmetic - two boys starting from the same place walk at a rate of 5 kmph and 55 kmph respectively what time will they take to be 85 km apart if they walk in the same direction - skillgun

In this type of questions we need to get the relative speed between them,
The relative speed of the boys = 5.5kmph – 5kmph
= 0.5 kmph
Distance between them is 8.5 km
Time = Distance/Speed
Time= 8.5km / 0.5 kmph = 17 hrs