4. Where is it cheaper? In one store, milk became cheaper by $40 \%$, and in another, it first became cheaper by $20 \%$, and then by another $25 \%$. Where did the milk become cheaper? The initial price of milk in each store was the same.
4. Let the initial price of milk be $x$ rubles. In the first store, it became $40 \%$ cheaper, that is, $0,6 x$ rubles. In the second store, after the first reduction, the milk cost $0,8 x$, and after the second reduction, $0,8 x \cdot 0,75=0,6 x$ rubles. Thus, the milk in each of the stores is once again priced the same.