There are 300 seniors at Morse High School, and 40% of them have cars. Of the remaining grades (freshmen, sophomores, and juniors), only 10% of them have cars. If 15% of all the students at Morse have cars, how many students are in those other three lower grades?
Pick one
A) 600
B) 900
C) 1200
D) 1350
E) 1500
Let the total no of students be n.   The no of seniors having cars is 40% of 300 i.e. 120.   The rest of the students with other three grades who have cars is 10% of (n-300).   The total no of students with cars is 15% of n.   Thus, 0.15n= 120+0.1(n-300)   On solving this, we get n=1800.   Hence, the no of students with other three grades is 1800-300, i.e. 1500 (1500).
<result>E</result>
There are 300 seniors at Morse High School, and 40% of them have cars. Of the remaining grades (freshmen, sophomores, and juniors), only 10% of them have cars. If 15% of all the students at Morse have cars, how many students are in those other three lower grades?