Question

Let $x,y,z$ and $w$ be whole numbers. Then the number of $4$ digit numbers ${}^{\prime }xyz{w}^{\prime }$ that can be formed such that $x<y$ and $z>w$ is

• A. $1,008$
• B. $1,296$
• C. $1,620$
• D. $2,025$

Answer 1

Answer: (C)

$N={}_{}^9{C}_2^{}\cdot {}_{}^{10}{C}_2^{}$