下面就是今天
2016年4月15日SAT数学题
An art gallery displays a large painting in the center of a wall that is 24 feet (ft) end text right parenthesis wide. The painting is 10ft wide. Which of the following equations can be used to find the distance, x, in feet, from either end of the wall to the corresponding edge of the painting?
A. |x-10|=12
B. 2|x-12|=10
C. 2|x-10|=12
D. |x-12|=10
解释：
Choice B is correct.The center of the wall is a distance of 1/2*(24)=12 feet from the left end of the wall. If x is the distance from a painting edge to its corresponding end of the wall, then |x-12| is the distance from the painting edge to the center of the wall.
If the painting is centered, then 2|x-12| represents the width of the painting.
Since the painting is 10ft wide, we have 2|x-12|=10.
正确答案是B。
2016年4月11日SAT数学题
The time it takes Erica to run one mile decreased consistently throughout her track season. She estimates that her time to run a one-minute mile decreased by about 15 seconds for every 2 weeks into the season. If Erika ran one mile in 500 seconds at the start of the season, and x weeks after the start of the season ran one mile in 425 seconds, which of the following equations best represents this context?
A. 500-7.5x=425
B. 500-15x=425
C. 500+7.5x=425
D. 500+15x=425
解释：
Choice A is correct. The time it took Erica to run one mile decreased by about 15 seconds for every 2 weeks of the season. This is equivalent to a decrease of 7.5 seconds every week.
If Erika trains for x weeks, 7.5x represents the total time, in seconds, that she has shaved off the time it took her to run one mile.
Subtracting this from her starting time gives the approximate time (in seconds) it takes her to run one mile at week x.
500-7.5x
Since it takes her 7 minutes and 5 seconds, or 425 seconds to run a mile after x weeks of the season, we can create the following equation:
500-7.5x=425
The equation that best represents the context is 500-7.5x=425.
正确答案是A。
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