The answer is 15, not 56.
When running in the same direction : If the ratio of speeds of two athletes (in the most reducible form) is a : b, the number of distinct meeting points on the track would be would be |a – b|
A and B will meet at |1 - 2| = 1 point.
A and C will meet at |1 - 3| = 2 points
A and D will meet at |1 - 4| = 3 points
A and E will meet at |1 - 5| = 4 points
A and F will meet at |1 - 6| = 5 points
A and G will meet at |1 - 7| = 6 points
So the distinct points are only 4+5+6=15.
Because 1,2,3 points coincide with 6 distinct points.
still not convinced?
draw a circle of 420 m and try plotting distinct points.you will 100% understand.