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Since the answer doesn’t depend on the value of x(the probability will be the same no matter what x is), let x = 1. Then the area of the whole square is 3² = 9. The area of each shaded triangle or of all the white sector can be calculated, but there’s an easier way: notice that if you slide the four shaded triangles together, They form a square of side 1. Therefore the total shaded side is, and so the shaded area is 1/9 of the total area and the probability that the chosen point is in the shaded area is  1/9 (A). The idea of subtracting a part from the whole works with line segments as well as areas.

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Solution
The entire region is a 2 × 5 rectangle whose area is 10. Since each white region is a quarter-circle of radius 2, the combined area of these region is that of a semicircle of radius 2: π (2) = 2π. Therefore, the area of the shaded region is
10 -2π = 2(5 – π) (B).

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Solution
Since Michael’s weight increase, his weight in 1990 was less than W. Eliminate
A, B, and C and guess. The answer is D
The Weight in 1990 is W/1.25 = 0.80W

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Use tactic A7 and assume that 100 copies were sold in 2002 (and 2004).
Sales dropped by 80 (80% of 100) to 20 in 2003 and then increase by 80, from
20 back to 100, in 2004. The percent increase was  actual increase/orignal amount× 100% = 80/20×
100% = 400% (D).

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