# SAT Math Multiple Choice Question 790: Answer and Explanation

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**Question: 790**

**10.** Anneke is competing in a 500-meter freestyle swim event, which consists of swimmingthe length of a pool 20 times. If Anneke averages 26.4 seconds per length of the pool,which of the following equations could be used to determine the number of meters (*m*) Anneke has left in the event after swimming for *s* seconds?

- A.
- B.
- C.
- D.

**Correct Answer:** A

**Explanation:**

**A**

**Difficulty:** Medium

**Category:** Heart of Algebra / Linear Equations

**Strategic Advice:** Make use of the given units to make sure your equation is set up properly.

**Getting to the Answer:** You're told that the units of *m* are meters, so you must find a way to combine the various quantities so that, when simplified, the result will be in meters as well. Anneke will swim 20 lengths in the 500-meter event, which means each length of the pool is = 25 m. Because each length is 25 m and Anneke can swim one length in 26.4 seconds on average, her average speed is m/s. Multiplying this quantity by *s*, the elapsed race time in seconds, will eliminate seconds from the units. The quantity *s* can therefore be subtracted from 500 (which is in meters) to yield the number of meters Anneke has remaining, making the final equation *m* = 500 -. (A) is the correct answer.