What problem would be created by using classes of 60-120, 120-can someone explain ?

  Class boundaries need to be defined so that a point on the boundary is unambiguously placed in one class or the other. With these boundaries, a value of 120 might be placed in the first or the second class—we don't know which.

It is customary to define class boundaries between data values 60.5–120.5, for example, so that no data value can fall on the boundary, or as a semi-open interval [60, 120), so that a boundary value is clearly placed into a specific class.

ryan had a head start of 10 meters.