SAT数学练习题—问答题 (11)

2016-02-25 11:53:02来源：网络

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　　SAT数学填空题练习题11参考答案

　　1.Correct Answer: 6

　　Explanation:

　　The area of the rectangle is 3x²

　　Area of right isosceles triangle = ½ x²

　　Divide the area of the rectangle by the area of the triangle

　　3x²/ ½ x² = 6　　2.Correct Answer: 3

　　Explanation:

　　n must be a factor if the result of dividing 81 by n is a whole number.

　　Factorize 81 to give factors of 9, 3, 27

　　Therefore n can take 3 different values

　　3.Correct Answer: 54

　　Explanation:

　　Draw out the figure and add a perpendicular height from the base.

　　Since area = ½ base x height, and area = 108

　　108 = 12 x height = 9

　　Now you need to recognize that each triangle formed by half the base, the height and the side marked �a�, is a 3-4-5 right triangle. Therefore �a� = 15

　　Perimeter of the large triangle = 24 + 15 + 15 = 54

　　4.Correct Answer: 50

　　Explanation:

　　Frame an equation. Let the number of $2.50 packs be n. the number of 410 packs sold = 75 - n.

　　Total cost = n (2.5) + (75-n)10

　　375 = 2.5n + 750 - 10n

　　7.5n = 375; n = 50

　　5.Correct Answer: 5

　　Explanation:

　　Half the perimeter = length + breadth = 7

　　The length = 2/7 x 14 = 4; the breadth = 7 - 4 = 3

　　The length and the breadth form the legs of a 3-4-5 right triangle with the diagonal of the rectangle forming the hypotenuse. So the diagonal = 5

　　6.Correct Answer: 189

　　Explanation:

　　We have a choice of 1/7 for a, 1/3 for b and 1/9 for c. Therefore we have 7 x 3 x 9 = 189 possible code names. (You multiply the choices because any one from a set can be combined with any from the other sets)

　　7.Correct Answer: 5/9

　　Explanation:

　　If one third is full, then 2/3 is empty initially. One third of the mixture that is to be added is ethanol. Therefore we are adding 1/3 x 2/3 ethanol = 2/9

　　But the flask already has 1/3 ethanol. New fraction will be 1/3 + 2/9 = 5/9

　　8.Correct Answer: 6.24

　　Explanation:

　　Draw a sketch. The points of intersection will lie symmetrically: one will be x units to the right of the center of the circle and one will be x units to the left. The x-coordinate of the center of the circle is 4, and so 1.76 lies (4 � 1.76) = 2.24 units to the left and the other point will lie 2.24 units to the right = 4 + 2.24 = 6.24

　　9.Correct Answer: 6

　　Explanation:

　　First simplify by taking out the brackets: a²b6/2 =108 ; a²b³ = 108

　　Now we are stuck unless we realize that if a and b are both integers there is probably only one solution to this equation, which we should be able to find if we find the prime factors of 108.

　　108 = 2 x 2 x 3 x 3 x 3 x 3, and so a must be 2 and b must be 3. Hence, ab = 6

　　10.Correct Answer: 5.39

　　Explanation:

　　Angles DAB and ABC are right angles. Because the areas of the circles are in the ratio of 4:1 the radii must be in the ratio of √4:√1 which is 2: 1. We are told the radius (BC) of the larger circle is 4, hence, the radius of the smaller circle must be 2.

　　If we draw a line from D perpendicular to BC we divide ABCD into a rectangle and a right triangle. The right triangle has sides 5 (because it is equal to AB), 2 (half of BC), and DC. Using Pythagoras theorem we have 5² + 2² = DC² DC = √29 = 5.3852 To three significant figures this is 5.39 (We can not grid in more anyway)

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