Each no.comes atleast twice:
Case a)Three nos. twice each
Take three numbers from the given set,lets take 1,2,3:
Now ways of arranging them :6P3/2*2*2
Since three are to be chosen for this purpose,we have5C3.
Total:6P3*5C3
Case b)Two nos thrice each:
Same way as above,6P2*5c2/3*3
Case c)One no:
no. of cases: 5
Adding everything,I get 255.
Please tell me if I've made an error !
Moderation Team
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