Isn’t X divided by lXl always one?

No, try X = -3 for instance.

thank you . I have another doubt. How to solve the data interpretation question 25 (page 98) of test 2, section 5 of the gre big book ?

Copy the question here.

Divide the total national health expenditures by the per-capita (which means the expenses per person).

So A goes in and B goes out. So in that case, if x is the rate for B,

2\times 96 - x \times 96 = 64

96(2 - x) = 64

2 - x = \frac{2}{3}

x = \frac{4}{3}

thank you