There are five comics numbered from 1 to 5. In how many ways can they be arranged, so that part-1 and part-3 are never together?

A.

48

B.

72

C.

120

D.

210

• The total number of ways in which 5 part can be arranged = 5! = 120.
  
  The total number of ways in which part-1 and part-3 are always together: = 4! × 2! = 48.
  
  Therefore, the total number of arrangements, in which they are not together, is: = 120 − 48 = 72.
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