Method-2

Let department members are: A, B, C, D, and E and A and B refuse to attend the conference together.

Hence, Total cases in which we A and B can be there in a pair:

• Both A and B are in the pair OR

• A is in the pair and B is not in the pair

• B is in the pair and A is not in the pair

• Neither of A or B is in the pair.

But,

out of all the cases we are not selecting 1 case:- When both A and B are in the pair.Thus, if we remove the case when both A and B are in the pair from the total pairs, we will get the answer.

• Total Pairs: \(^5c_2\)

• Total Pairs when both A and B are in the pair= 1

Thus, required answer= 10-1

Hence, total ways=9

Hence, the correct answer is option B.

Answer: B
_________________

Register for free sessions

Number Properties | Algebra |Quant Workshop

Success Stories

Guillermo's Success Story | Carrie's Success Story

Ace GMAT quant

Articles and Question to reach Q51 | Question of the week

Must Read Articles

Number Properties – Even Odd | LCM GCD | Statistics-1 | Statistics-2 | Remainders-1 | Remainders-2

Word Problems – Percentage 1 | Percentage 2 | Time and Work 1 | Time and Work 2 | Time, Speed and Distance 1 | Time, Speed and Distance 2

Advanced Topics- Permutation and Combination 1 | Permutation and Combination 2 | Permutation and Combination 3 | Probability

Geometry- Triangles 1 | Triangles 2 | Triangles 3 | Common Mistakes in Geometry

Algebra- Wavy line | Inequalities

Practice Questions

Number Properties 1 | Number Properties 2 | Algebra 1 | Geometry | Prime Numbers | Absolute value equations | Sets

| '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com