每日一题

Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

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

答案和解析

答案：A

解析：

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.