A and B run on a circular path of perimeter 1200 m at different speeds. If they start at the same time and from the same place, but run in opposite directions, they meet for the first time in 3 minutes. If the speed of B is 10.8 km/h, then what is the speed (in km/h) of A?
- A12.8
- B13.2
- C12.5
- D13.5
Solution & Step-by-step Explanation
Perimeter of the path = 1200 m.
Time taken to meet = 3 minutes=3×60=180 seconds.
Since they run in opposite directions, their relative speed is (S
A
+S
B
).
Relative Speed=
Time
Distance
=
180
1200
=
3
20
m/s
Convert relative speed into km/h:
Relative Speed in km/h=
3
20
×
5
18
=4×6=24 km/h
Given speed of B = 10.8 km/h:
S
A
+S
B
=24
S
A
+10.8=24⟹S
A
=24−10.8=13.2 km/h
Time taken to meet = 3 minutes=3×60=180 seconds.
Since they run in opposite directions, their relative speed is (S
A
+S
B
).
Relative Speed=
Time
Distance
=
180
1200
=
3
20
m/s
Convert relative speed into km/h:
Relative Speed in km/h=
3
20
×
5
18
=4×6=24 km/h
Given speed of B = 10.8 km/h:
S
A
+S
B
=24
S
A
+10.8=24⟹S
A
=24−10.8=13.2 km/h