On five chairs arranged in a row, five persons A, B, C, D and E are to be seated in such a way that B and D always sit together (side by side). In how many different ways can it be done ?
Consider B and D to be one unit. So, there are a total of 4 units - A, BD, C and E. These can be arranged in 4! = 24 ways
B and D can be arranged among themselves in 2! = 2 ways
So, total number of ways of arrangement = 24*2 = 48 ways
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