AMC 10/12 Student Practice Questions Guide to Student Practice Questions
Each of the following four large congruent squares is
subdivided into combinations of congruent triangles or
rectangles and is partially shaded. What percent of the total
area is partially shaded?
I
The original problem
and choices from the
2011 AMC 8 contest
(A) 12 (B) 20
(C) 25 (D) 33 (E) 37

Step-by-step explanation:

Notice how each congruent square is divided into four equal parts. Since each square has four parts and there are four squares, there are of these parts in total. Because each of these parts make up of each square, all parts are equal. Therefore, you can count the total number of shaded parts to get your percentage.

The top left and bottom right both have one part shaded each for a total of parts.

The top right and bottom left have and parts shaded, respectively, for a total of parts.

Therefore, in total, there are parts shaded out of total parts.

Thus, the percentage of the total area that is shaded is:

.

thus, the first answer choice, y = sec x, is the correct one

6

step-by-step explanation: