The number of possibilities if all the dice look different is 6^4
Only 6 of those will have every cie the sames
So P(all the same number )= $${\frac{{\mathtt{6}}}{{{\mathtt{6}}}^{{\mathtt{4}}}}} = {\frac{{\mathtt{1}}}{{\mathtt{216}}}} = {\mathtt{0.004\: \!629\: \!629\: \!629\: \!629\: \!6}}$$
P (they are not all the same) = $${\mathtt{1}}{\mathtt{\,-\,}}\left({\frac{{\mathtt{6}}}{{{\mathtt{6}}}^{{\mathtt{4}}}}}\right) = {\frac{{\mathtt{215}}}{{\mathtt{216}}}} = {\mathtt{0.995\: \!370\: \!370\: \!370\: \!370\: \!4}}$$
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