Question

Let $S=\{1,2,3,4,5,6\}$. Then the number of one-one functions $f:S→P(S)$, where $P(S)$ denote the power set of $S$, such that $f(m)⊂f(m)$ where $n<m$ is _______

Answer 1

Answer: 3240

Let $S=\{1,2,3,4,5,6\}$, then the number of one-one functions, $f:Sâ‹\dots P(S)$, where $P(S)$ denotes the power set of $S$, such that $f(n)<f(m)$ where $n<m$ is
$n(S)=6$
$P(S)=\left\{\begin{array}{c}ϕ,\{1\},…\{6\},\{1,2\},…,\\ \{5,6\},…,\{1,2,3,4,5,6\}\end{array}\right\}$
$−64$ elements
case $−1$
$f(6)=S$ i.e. 1 option,
$f(5)=$ any 5 element subset $A$ of $S$ i.e. 6 options,
$f(4)=$ any 4 element subset $B$ of $A$ i.e. 5 options,
$f(3)=$ any 3 element subset $C$ of $B$ i.e. 4 options,
$f(2)=$ any 2 element subset $D$ of $C$ i.e. 3 options,
$f(1)=$ any 1 element subset $E$ of $D$ or empty subset i.e. 3
options,
Total functions $=1080$
Case $−2$
$f(6)=$ any 5 element subset $A$ of $S$ i.e. 6 options,
$f(5)=$ any 4 element subset $B$ of $A$ i.e. 5 options,
$f^{′}(4)=$ any 3 element subset $C$ of B i.e. 4 options,
$f(3)=$ any 2 element subset $D$ of $C$ i.e. 3 options,
$f^{′}(2)=$ any 1 element subset $E$ of $D$ i.e. 2 options,
$f(1)=$ empty subset i.e. 1 option
Total functions $=720$
Case $−3$
$f(6)=S$
$f(5)=$ any 4 element subset $A$ of ' $S$ i.e. 15 options,
$f(4)=$ any 3 element subset $B$ of $A$ i.e. 4 options,
$f(3)=$ any 2 element subset $C$ of $B$ i.e. 3 options,
$f(2)=$ any 1 element subset $D$ of $C$ i.e. 2 options,
$f(1)=$ empty subset i.e. 1 option
Total functions $=360$
Case $−4$
$f(6)=S$
$f(5)=$ any 5 element subset $A$ of $S$ i.e. 6 options,
$f(4)=$ any 3 element subset $B$ of $A$ i.e. 10 options,
$f(3)=$ any 2 element subset $C$ of $B$ i.e. 3 options,
$f(2)=$ any 1 element subset $D$ of $C$ i.e. 2 options,
$f(1)=$ empty subset i.e. 1 option
Total functions $=360$
Case $−5$
$f(6)=S$
$f(5)=$ any 5 element subset $A$ of $S$ i.e. 6 options,
$f(4)=$ any 4 element subset $B$ of $A$ i.e. 5 options,
$f(3)=$ any 2 element subset $C$ of $B$ i.e. 6 options,
$f(2)=$ any 1 element subset $D$ of $C$ i.e. 2 options,
$f(1)=$ empty subset i.e. 1 option
Total functions $=360$
Case $−6$
$f(6)=S$
$f(5)=$ any 5 element suhset $A$ of $S$ i e 6 options
$f(4)=$ any 4 element subset $B$ of $A$ i.e. 5 options,
$f(3)=$ any 3 element subset $C$ of $B$ i.e. 4 options,
$f(2)=$ any 1 element subset $D$ of $C$ i.e. 3 options,
$f(1)=$ empty subset i.e. 1 option
Total functions $=360$
$∴$ Number of surch funstions $=3240$