Given
\(1.1x\)
\(0.9y\)

\(\frac{0.9y}{x}\cdot 100 = ¿?\)

THE KEY: This is a COMBO QUESTION \(\Rightarrow\) Knowing \(\frac{y}{x}\) (or knowing that you have sufficient information to know \(\frac{y}{x}\)) is sufficient.


Statement 1:
\(1.1x = y\,\Rightarrow\,\frac{y}{x}=1.1\). Sufficient.

Statement 2:
\(0.1x = \frac{10}{11}\cdot 0.1y\,\Rightarrow\,\frac{y}{x}=1.1\). Sufficient.

Note the difference between:
- the increase IN THE price of \(x \,\Rightarrow\, 0.1x\)
- the decrease IN THE price of \(y \,\Rightarrow\, 0.1y\)
- the INCREASED price in \(x \,\Rightarrow\, 1.1x\)
- the DECREASED price in \(y \,\Rightarrow\, 0.9y\).

Therefore, __D__ is the correct option.