Past exam of the options I course of the University of Oxford / 2004 / O / O1 / ii

Separate high-count classes have very small expected frequencies, making the chi-square approximation unreliable. Pooling the upper tail gives a class with expected count about $20.9$, comfortably above the customary small-cell threshold. The pooling protects the asymptotic test approximation, while retaining the tail count as part of the goodness-of-fit comparison.