\(2:1:1\)
To determine the updated profit-sharing ratio subsequent to Kunal's admission, we commence with the pre-existing ratio between Aman and Riya, which is 5:3. This establishes Aman's share as \( \frac{5}{8} \) and Riya's share as \( \frac{3}{8} \) of the total profit.
Kunal is admitted with a \( \frac{1}{4} \) share, sourced equally from Aman and Riya. Consequently, both Aman's and Riya's individual shares will be reduced by \( \frac{1}{8} \), derived from \( \frac{1}{4} \div 2 = \frac{1}{8} \).
The calculation of the revised shares is as follows:
To ascertain the new ratio, we express the fractions \(\frac{1}{2}\), \(\frac{1}{4}\), and \(\frac{1}{4}\) with a common denominator of 4:
Therefore, the new profit-sharing ratio among Aman, Riya, and Kunal is established as \(2:1:1\).

