# Algebra: What percent of the apartments with windows have hardwood floors?

Algebra is by far the most fundamental question type appearing on GMAT, GRE, or SAT. This topic encompasses subtopics such as Algebraic Expressions, Linear Equations, Quadratic Equations, Exponents, Inequalities, Absolute Value, and Functions.
One would often find good chunk of word problems appearing from this topic. It also covers arguably the most dreaded combination on these exams – Inequality + Data Sufficiency.
Like Number Systems, Algebra forms the basis for many question types on the test and there are many smart tricks to be learnt.  One should learn how to avoid pitfalls, and be careful in dealing certain question types. This topic must be tamed with supreme authority to do well on the Maths section.
Solve the following question:

50% of the apartments in a certain building have windows and hardwood floors. 25% of the apartments without windows have hardwood floors. If 40% of the apartments do not have hardwood floors, what percent of the apartments with windows have hardwood floors?
A) 10%
B) 16.66%
C) 40%
D) 50%
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