P, Q, R and S start from the same point to walk around in a circular path, in the same direction, around a garden whose circumference is one kilometre. P walks 5 km an hour, Q walks 4 km an hour, R walks 7 km an hour and S walks 11 km an hour. How long will it take all four to meet again at the starting point?
1
3 hours
2
2 hours
3
1 hour
4
4 hours