In a differential mechanism, two equal sized bevel wheels \(A\) and \(B\) are keyed to the two halves of the rear axle of a motor car. The car follows a curved path. Which one of the following statements is correct?

The wheels \(A\) and \(B\) will resolve at different speeds and the casing will revolve at a speed which is equal to the

(a) difference of speeds of \(A\) and \(B\)

(b) arithmetic mean of the speeds \(A\) and \(B\)

(c) geometric mean of the speeds of \(A\) and \(B\)

(d) harmonic mean of the speeds \(A\) and \(B\)