In the faculty of Reverse-Engineering, 240 second year students study numeric methods, 423 second year students study automatic control of airborne vehicles and 134 second year students study them both. How many students are there in the faculty if the second year students are approximately 80% of the total?
Choose the correct choice from the following options: A) 515 . B) 545 . C) 661 . D) 644 . E) 666 .

Rationale: "answer is c : 661 solution : total number of students studying both are 423 + 240 - 134 = 529 ( subtracting the 134 since they were included in the both the other numbers already ) . so 80 % of total is 529 , so 100 % is approx . 661 ."
Answer: C