There are 640 students in a school. The ratio of boys and girls in this school is 3:5. Find the total of girls & boys are there in this school?  Answers:
A) 320  B) 345  C) 375  D) 380  E) 400

Rationale: "in order to obtain a ratio of boys to girls equal to 3 : 5 , the number of boys has to be written as 3 x and the number of girls as 5 x where x is a common factor to the number of girls and the number of boys . the total number of boys and girls is 640 . hence 3 x + 5 x = 640 solve for x 8 x = 640 x = 80 number of boys 3 x = 3 × 80 = 240 number of girls 5 x = 5 × 80 = 400 e"
Answer: E