A and B start from the same point and in the same direction at 7 am to walk around a rectangular field 400 m × 300 m. A and B walk at the rate of 3 km/hr and 2.5 km/hr respectively. How many times shall they cross each other if they continue to walk till 12.30 pm ?

A and B start from the same point and in the same direction at 7 am to walk around a rectangular field 400 m × 300 m. A and B walk at the rate of 3 km/hr and 2.5 km/hr respectively. How many times shall they cross each other if they continue to walk till 12.30 pm ? Correct Answer Once

Perimeter of the field
= 2(400 + 300) m
= 1400 m
= 1.4 km
Since A and B move in the same direction, so they will first meet each other when there is a difference of one round i.e., 1.4 km between the two.
Relative speed of A and B = (3 - 2.5) km = 0.5 km/hr
Time take to cover 1.4 km at this speed :
$$\eqalign{ & = \left( {\frac{{1.4}}{{0.5}}} \right){\text{ hr}} \cr & = 2\frac{4}{5}{\text{ hr}} \cr & = 2{\text{ hr 48 min}} \cr} $$
So, they shall first cross each other at 9.48 am
And again 2 hr 48 min after 9.48 am i,e., 12.36 pm
Thus, till 12.30 pm they will cross each other once.

Related Questions

How far is point 'R' from Point 'T'? Statement (I): Point 'R' is 5 metres to the north of point 'M'. Point 'U' is 4 metres to the east of point 'R'. Point 'T' is to the west of point 'R' such that points 'U' 'R' and 'T' form a straight line of  metres. Statement (II): Point 'Z' is metres to the south of point 'T'. Point 'U' is  metres to the east of point 'T'. Point 'M' is  metres to the east of point 'Z'. Point 'R' is  metres to the north of point 'M'. Point 'R' lies on the line formed by joining points 'T' and 'U'.