Question

suppose A1, A2,....,A30 are 30 sets each with 5 elements and B1, B2,...., Bn are n sets each with 3 elements. let union ofA1, A2,....,A30 = union ofB1, B2,...., Bn =S. Each element of S belongs to 10 of A's and 9 of B's. find n.

Answer 1

The number of elements has been considering with the union and set includes number of repeats.

This should focus on determining the unions that has been set with S in 10 sets that includes 9 bsets.

Each element must be taken in the union and known for S belongs to exactly 10 of the AIs.