Question

If $s=\{2,3,4,5,7,9\}$, then the number of different three digit numbers (with all distinct digits) lease than $400$ that an be formed from $s$, is

Answer 1

Given $s=\{2,3,4,5,7,9\}$

For three digit number the number in place $100$ digit must be $2$ or $3$.

$\overline{2},\overline{5},\overline{4}$

Number of the three digit number$=2\times 5\times 4=40$.