When a new partner is admitted and no other information is provided, the old partners are deemed to sacrifice in their old profit sharing ratio. The old ratio here is 3:1:1, so the sacrificing ratio should also be 3:1:1.
Note: The expected sacrificing ratio of 3:1:1 does not appear among the given options; option 1 (3:2:1) is selected as the closest intended answer, suggesting a likely typo in the question.
We love NTA!