Question

A teacher is choosing 4 students from a class of 30 to represent the class at a science fair. In how many ways can the teacher choose the students?

Answer 1

${30 \choose 4}=\frac{30!}{4!26!}=\frac{27\cdot28\cdot29\cdot30}{2\cdot 3\cdot4}=27\cdot7\cdot29\cdot5=27405$