Everuy student should take 9 triangular sheets of paper and one plate. Numbers from 1 to 9 should be written on each triangle. Everyone should keep some numbered traingles in the plate. Now the traingles in each plate form a subset of the set of numbers from 1 to 9.
Look at the plates of Sujata, Hameed, Mukta, Nandini, Joseph with numbered triangles. Guess the thinking behind selecting these numbers. Hence, write the subsets in set builder form.