d2: q3:The no of different 7 digit nos that can be written using only 3 digits 1,2&3 under the condition that the digit 2 occurs exactly twice in each no is?

Dear jee king

first select the 2 position out of 7 position and put 2 there =⁷C₂ ways

and rest 5 position can be filled by 2 ways either by 1 or 3

so total ways

= ⁷C₂ *2*2*2*2*2 =672 ways

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