Question
None of the digits are repeated?
Answer: Option B
:
B
When none of the digits are repeated:The hundred’s place can be filled by any of the digits: 2, 3, 5, 6, 7 or 8 except the one which has already been used at the thousand’s place, so it can be filled in 5 ways.Similarly tens’ place can be filled in 4 ways: only those 4 numbers which have not been use either at hundred’s or thousand’s place.Unit’s place can be filled in only 3 ways.So, total number of nos. Possible = 4* 5*4*3 = 240Hence option (b)
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:
B
When none of the digits are repeated:The hundred’s place can be filled by any of the digits: 2, 3, 5, 6, 7 or 8 except the one which has already been used at the thousand’s place, so it can be filled in 5 ways.Similarly tens’ place can be filled in 4 ways: only those 4 numbers which have not been use either at hundred’s or thousand’s place.Unit’s place can be filled in only 3 ways.So, total number of nos. Possible = 4* 5*4*3 = 240Hence option (b)
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