Question
Mon October 31, 2011 By:

the no. of different 7 digit no.s 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?

Expert Reply
Tue November 01, 2011
Since 2 occurs exactly twice in each arrangement,
So the number of arrangements for the 2 positions where 2 appears = 1*1= 1
Number of arrangement for remaing five positons  where 1 and 3 appears = 2*2*2*2*2 = 32
Hence total number of arrangements = 1*32 = 32
Ask the Expert