There are 300 seniors at Morse High School, and 50% of them have cars. Of the remaining grades (freshmen, sophomores, and juniors), only 10% of them have cars. If 25% of all the students at Morse have cars, how many students are in the three lower grades?  Choose the correct choice from the following options.
A) 500	B) 900	C) 1200	D) 1350	E) 1500
Let x be the number of students in the lower three grades.   0.1x + 150 = 0.25(x+300)   0.15x = 75   x = 500   The answer is 500.
<result>A</result>
There are 300 seniors at Morse High School, and 50% of them have cars. Of the remaining grades (freshmen, sophomores, and juniors), only 10% of them have cars. If 25% of all the students at Morse have cars, how many students are in the three lower grades?