Answer:
35 ways
Step-by-step explanation:
Alex has 9 friends and wants to invite 5 friends. Since Alex requires two of his friends who are twins to come together to his birthday party, since the two of them form a group, the number of ways we can select the two of them to form a group of two is ²C₂ = 1 way.
Since we have removed two out of the nine friends, we are left with 7 friends. Also, two friends are already selected, so we are left with space for 3 friends. So, the number of ways we can select a group of 3 friends out of 7 is ⁷C₃ = 7 × 6 × 5/3! = 35 ways.
So, the total number ways we can select 5 friend out of 9 to party come to the birthday include two friends is ²C₂ × ⁷C₃ = 1 × 35 = 35 ways
