Mathematics - Functions Question with Solution | TestHub

Let ${\mathrm{A}}_1,{\mathrm{A}}_2,{\mathrm{A}}_3,\dots ,{\mathrm{A}}_{40}$ are 40 sets each with 7 elements and ${\mathrm{B}}_1,{\mathrm{B}}_2,\dots ,{\mathrm{B}}_{\mathrm{n}}$ are n sets each with 7 elements. If ${\bigcup }_{i=1}^{40}{A}_i={\bigcup }_{j=1}^n{B}_j=S$ and each element of $S$ belongs to exactly ten of $A_i$ ' and exactly 9 of $B_{\mathrm{j}}$ 's, then $n$ equals