Question

$A$ and $B$ are non-singleton sets and $n(A\times B)=35.$ If $B\subset A$ then ${}^{n\left(A\right)}{C}_{n\left(B\right)}=$

• A. 28
• B. 35
• C. 42
• D. 21

Answer 1

Answer: (D)

$n(A\times B)=35=7\times 5,7_{C_5}=7_{C_2}=21$