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SAT数学选择题

发布时间:2017-08-17编辑:Misrong
1.The population of Norson, the largest city in Transitania, is 50percent of the rest of the population of Transitania. The population of Norson is what percent of the entire population of Transitania? 

  (A) 20%

  (B) 25%

  (C) 30%

  (D) 33 and (1 over 3)%

  (E) 50%

  2.If 2^a = 4^b, which of the following expresses a in terms of b?

  Answer Choices

  (A) b over 2

  (B) b

  (C) 2 times b

  (D) 4 times b

  (E) 2^b

math image

   3.In the figure above, x = 60and y = 40. If the dashed lines bisect the angles with measures of x degreesand y degrees, what is the value of z

  (A) 25

  (B) 35

  (C) 40

  (D) 45

  (E) 50

  4.A mechanic can install carburetors in 3 cars every 4 hours. At that rate, how long will it take the mechanic to install carburetors in 5 cars?

  (A) 6 hr 20 min

  (B) 6 hr 40 min

  (C) 7 hr 15 min

  (D) 7 hr 30 min

  (E) 7 hr 45 min

  Explanation

  1.The correct answer is D

  Let Nequal the population of Norson, and let Tequal the entire population of Transitania. Then T minus Nis the population of the rest of Transitania. Nis 50%of (T minus N)

  N = (1 over 2) times (T minus N), or 2 times N = T minus N.

  This gives 3 times N = T, or N = (1 over 3) times T

  So the population of Norson is one third, or 33 and (1 over 3)%, of the entire population of Transitania. 

  2.The correct answer is C

  Choice (C) is correct. Since 4 = 2^2, it follows that 4^b = (2^2)^b = 2^(2 times b). Therefore, 2^a = 4^b = 2^(2 times b), from which it follows that a = 2 times b.

  3.The correct answer is E

Image

 

  First, add the labeled points A, B, C, D, E, and Oto the figure, as shown above. Then segment line O Bbisects angle A O C, so measure of angle A O B = measure of angle B O C, and measure of angle A O B + measure of angle B O C = x degrees = 60 degrees. Thus, measure of angle A O B = measure of angle B O C = 30 degrees. Similarly, measure of angle C O D = measure of angle D O E = 20 degrees, because angle C O Dand angle D O Eare of equal measure and the sum of their measures is y degrees = 40 degrees. From the figure, it follows that z degrees = measure of angle B O C + measure of angle C O D = 30 degrees + 30 degrees = 50 degrees. Therefore, z = 50.

  4.The correct answer is B

  From the information given, you can write the proportion 3 cars is to 4 hours as 5 cars is to x hours, where x represents the number of hours the mechanic will take to install carburetors in 5 cars. This gives 3 cars over 4 hours = 5 cars over x hours, which simplifies to 3 times x = 4 times 5 = 20. Therefore, x = 20 over 3 = 6 and (2 over 3) hours. Since 2 over 3 hour is 40 minutes, x is 6 hours 40 minutes.

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