7. Students have three types of number cards: $1$, $2$, and $3$, with many cards of each type. The teacher asks each student to take out two or three number cards to form a two-digit or three-digit number. If at least three students form the same number, then these students have at least  people.
【Answer】 73 people
【Key Point】Pigeonhole Principle
【Analysis】
The different two-digit numbers that students can form are $3 \times 3=9$, and the different three-digit numbers that students can form are $3 \times 3 \times 3=27$. Therefore, the total number of different numbers that students can form is $9+27=36$; If we want to ensure that at least three students form the same number, then there must be at least $2 \times 36+1=73$ students.