Sunil and Ravi are partners in a firm sharing profits in the ratio of $3:1$. Amar is admitted for $\frac{1}{4}$ share. The sacrificing ratio of Sunil and Ravi is:

In a simple case of admission where a new partner is admitted for a specific fraction share and no explicit details are provided about how the new partner acquires their share from the old partners, the old partners sacrifice in their old profit-sharing ratio.Therefore, the sacrificing ratio between Sunil and Ravi is equal to their old ratio, which is $3:1$.