Question

how many 10 digit numbers can be formed using 3 and 7 only​

Answer 1

Given:

$10$ digit number and $2$ single digits $3$ and $7$

To find:

How many $10$ digit numbers can be made from $3$ and $7$

Solution:

There are $10$ digits to be filled by $3$ or $7$

So the first digit can be $3$ or $7$ so there are $2$ choices for $1st$ digit

The second digit can be $3$ or $7$ so there are $2$ choices for $2nd$ digit

The third digit can be $3$ or $7$ so there are $2$ choices for $3rd$ digit and so on.

So similarly, for the tenth digit also there are $2$ choices for $10th$ the digit

( $2$ digits choices for each digit) to the par of $10$

= $2^{10}$

Equals $1024$

Answer: 1024,  10 digit numbers can be formed using 3 and 7