The sum of the digits in the unit's place of | vedclass

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(B) To form a $4-$ digit number using the digits $3, 4, 5,$ and $6$ without repetition,we have $4! = 24$ total numbers.If we fix a digit at the unit's

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$108$

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(B) To form a $4-$ digit number using the digits $3, 4, 5,$ and $6$ without repetition,we have $4! = 24$ total numbers.If we fix a digit at the unit's place,the remaining $3$ positions can be filled by the remaining $3$ digits in $3! = 6$ ways.Therefore,each of the digits $3, 4, 5,$ and $6$ appears in the unit's place exactly $6$ times.The sum of the digits in the unit's place is:$= (6 	imes 3) + (6 	imes 4) + (6 	imes 5) + (6 	imes 6)$$= 6 	imes (3 + 4 + 5 + 6)$$= 6 	imes 18$$= 108$

The sum of the digits in the unit's place of all the $4-$ digit numbers formed by using the digits $3, 4, 5,$ and $6$,without repetition,is:

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