Aptitude

Question

The number of positive numbers of not more than 10 digits formed using 0,1,2,3?

Answer 1

1. Number of 1 digit numbers = 3                (1,2,3)              [ 0 cannot taken not positive]
2. Number of 2 digit numbers = 3$\times$4     (1st place 3 number , last place any of 4 dgits)  [ 0 cannot taken on 1st place]
3. Number of 3 digit numbers = 3$\times$4²

Like this do till 9 digits = 3 $\times$4⁰ + 3 $\times$4¹+ 3 $\times$4²+...................+ 3 $\times$4⁹

Solving this we get = $\frac{3 \times (4^{10} -1)}{4-1}$ = 4¹⁰-1

Comments

Nice explanation. And also i got my mistake .