= Solution
The expected counts in the final two separate classes are too small for a reliable <chi-squared asymptotic approximation>. Pooling the last three classes gives the tail class $\geq7$, with observed frequency $8+3+1=12$ and expected frequency $5.464+1.473+0.447=7.384$. This exceeds the usual expected-count guideline of 5. Pooling only the last two would leave an expected count of $1.920$, still too small. Pooling requires recomputing the contribution from the pooled totals, rather than adding the old separate contributions.
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