Question

Write all possible $2-\mathrm{digit}$ numbers formed by the digits $3,7$ and $9$, when repetition of digits is not allowed.

Answer 1

Here we have to form $2-\mathrm{digit}$ numbers using digits $3,7$ and $9$ using each digit only once in each number

Keeping $3$ at ones place, $2-\mathrm{digit}$ numbers are $73\mathrm{and}93$

Keeping $7$ at ones place, $2-\mathrm{digit}$ numbers are $37\mathrm{and}97$

Keeping $9$ at ones place, $2-\mathrm{digit}$ numbers are $79\mathrm{and}39$

Hence the required numbers are $73,93,37,97,79$ and $39$