Question

How many seven digit numbers are there when 0 , 5 and 6 cannot be the leading number?

Answer 1

so at first place u can fill 7 numbers

Answer 2

asit doesnt say repeating..so
7 *9*8*7*6*5......upto 7th place

Answer 3

\(\large\tt \begin{align} \color{black}{\text{seven digit numbers:} \\ ~\\

\text{1000000 to 9999999}\\~\\

\text{counting value is 9000000}\\~\\
\text{seven digit numbers leading with 5 and 6:}\\~\\
\text{5000000 to 5999999 and 6000000 to 6999999}\\~\\
\text{=5000000 to 6999999}\\~\\
\text{there counting value is 2000000}\\~\\

{therefore~~ 9000000-2000000=\color{green}{7000000}
}}\end{align}\)