From (10) teachers and (12) students a group of (7) people is to be formed with at least (3) teachers. How many ways are there?

Correct answer: 124872

The number of teachers in the group can be 3, 4, 5, 6, or 7. Hence, the total number of groups is \(\binom{10}{3}\binom{12}{4}+\binom{10}{4}\binom{12}{3}+\binom{10}{5}\binom{12}{2}+\binom{10}{6}\binom{12}{1}+\binom{10}{7}\binom{12}{0}\) = \(59400+46200+16632+2520+120=124872\). Therefore, option C is correct. Using only \(\binom{10}{3}\binom{12}{4}\) counts exactly 3 teachers, not at least 3 teachers. Exam tip: for “at least” conditions, add all the valid cases.