Question Number 70638 by abdusalamyussif@gmail.com last updated on 06/Oct/19
Commented by MJS last updated on 06/Oct/19
$$\mathrm{the}\:\mathrm{first}\:\mathrm{question}\:\mathrm{cannot}\:\mathrm{be}\:\mathrm{complete} \\ $$
Answered by mr W last updated on 06/Oct/19
$${Q}\mathrm{1}:\: \\ $$$${i}\:{don}'{t}\:{understand}\:{the}\:{question}. \\ $$$$ \\ $$$${Q}\mathrm{2}: \\ $$$${one}−{digit}\:{numbers}:\:{X} \\ $$$$\Rightarrow\mathrm{9}\:{numbers} \\ $$$${two}−{digit}\:{numbers}:\:{XY} \\ $$$$\Rightarrow\mathrm{9}×\mathrm{9}=\mathrm{81} \\ $$$${three}−{digit}\:{numbers}:\:{XYZ} \\ $$$$\Rightarrow\mathrm{9}×\mathrm{9}×\mathrm{8}=\mathrm{648} \\ $$$$ \\ $$$${totally}:\:\mathrm{9}+\mathrm{81}+\mathrm{648}=\mathrm{738}\:{numbers} \\ $$