SAT数学每日一练daily practice(2018年3月21日)

2018年3月21日的SAT数学每日一练如下：

Mathematics>Standard Multiple Choice

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

Lisa gives her little brother Sam a 15-second(sec) head start in a 300-meter(m) race. During the race, Sam runs at an average speed of 5 m/sec and Lisa runs at an average speed of 8 m/sec, notincluding the head start. Which of the following best approximates the number of seconds thathad passed when Lisa caught up to Sam?

以下哪一项最接近Lisa追到山姆时所经过的秒数?

A.5

B.25

C.40

D.55

正确答案：B

详细解析：

EXPLANATION

Choice B is correct. Let t represent the time, in seconds, that Sam spends running, let d represent the distance run, and let r represent the rate at which Sam is moving.

Then, since d equals r t, 5 t represents the total distance, in meters, Sam runs in t seconds.

Since Lisa gives her little brother a 15-second head start, it follows that she runs for t minus 15 seconds at a rate of 8 text m / sec end text.

So, 8 left parenthesis t minus 15 right parenthesis represents the total distance, in meters, Lisa runs in left parenthesis t minus 15 right parenthesis seconds.

If Lisa catches Sam, they would have covered the same distance. Therefore, we can set up the following equation and solve for t:

table attributes columnalign right left end attributes row cell 8 left parenthesis t minus 15 right parenthesis end cell cell equals 5 t end cell row cell 8 t minus 120 end cell cell equals 5 t end cell row cell 3 t end cell cell equals 120 end cell row t cell equals 40 end cell end table

Since t represent the time, in seconds, that Sam spends running, this shows that Sam will run for 40 text seconds end text before his sister catches him.

Since Lisa runs for t minus 15 seconds, it follows that she runs for 25 seconds before catching up with Sam.

以上就是为大家整理的3月21日的sat数学每日一练的内容。各位小可爱们，在备考的过程中，放松好心情，保持练题和模拟，有问题及时和老师或者同学进行沟通，小站sat数学频道会一直陪伴着你们哦，好好加油，小可爱们!向春天粗发~想了解更多SAT数学每日一练内容，请戳小站SAT数学首页~