A meeting has to be conducted with 5 managers. Find the number of ways in which the managers may be selected from among 7 managers, if there are 2 managers who refuse to attend the meeting together.
Choose the correct option
A) 6 B) 8 C) 10 D) 11 E) 15

Rationale: "the total number of ways to choose 5 managers is 7 c 5 = 21 we need to subtract the number of groups which include the two managers , which is 5 c 3 = 10 . 21 - 10 = 11 the answer is d ."
Answer: D