both blanks ask for a fraction, and the danger is the denominator. Each fraction is taken over a specific group, not over all six apartments, so the first job is to build the right group for each blank and count within it. The rent threshold is strict: premium means more than $2,000, so an apartment renting for exactly $2,000 is not premium.
Sort the six apartments two ways. Premium means rent above $2,000: A1 ($2,400), A3 ($3,000), and A4 ($2,200), which is three premium apartments. A6 rents for exactly $2,000, so it is not premium. Pet-friendly means yes in the third column: A1, A2, A4, and A6, which is four pet-friendly apartments. Two apartments are in both groups, A1 and A4, the premium ones that are also pet-friendly.
The premium-conditioned blank asks for the fraction of the premium apartments that are pet-friendly. The denominator is the three premium apartments. Of them, A1 and A4 are pet-friendly and A3 is not, so two of the three are pet-friendly, which is 2/3.
The pet-friendly-conditioned blank asks for the fraction of the pet-friendly apartments that are premium. Now the denominator switches to the four pet-friendly apartments, and two of them are premium, A1 and A4, so the fraction is 2/4, or 1/2.
The numerator is the same two apartments both times, A1 and A4, the ones in both groups, but the denominator is different, so the fractions are different. The sharpest trap is keeping one denominator for both blanks. If you divide by the three premium apartments both times you put 2/3 in both, and if you divide by the four pet-friendly apartments both times you put 1/2 in both. But the premium-conditioned blank is taken over the three premium apartments, giving 2/3, while the pet-friendly-conditioned blank is taken over the four pet-friendly apartments, giving 1/2, so the denominator switches with the conditioning direction.
The discipline: in 'of those who are X, the fraction who are Y,' the denominator is the X-group, not the whole table, and when the roles of X and Y switch between the blanks, the denominator switches with them.
Fraction of premium apartments that are pet-friendly: 2/3. Fraction of pet-friendly apartments that are premium: 1/2.