A person has 6 friends. He wants to invite at least one of his friends to his house.
He may invite his 1 friend or 2 friends or 3 friends or 4 friends or 5 friends or 6 friends out of his 6 friends.
∴ Total combinations
= 6C1 + 6C2 + 6C3 + 6C4 + 6C5 + 6C6
= 6 + \(\frac{6×5}{2×1}+\frac{6×5×4}{3×2×1}+\frac{6×5×4×3}{4×3×2×1}\) + 6 + 1
= 6 + 15 + 20 + 15 + 6 + 1 = 63
