R and S are currently sharing profits in a 4:1 ratio. When T is admitted, he gets 1/5 of the total share, and this share will be equally distributed between R and S.
- T’s share = \( \frac{1}{5} \)
Thus, the remaining share is \( 1 - \frac{1}{5} = \frac{4}{5} \).
Since R and S share this remaining \( \frac{4}{5} \) in the ratio of 4:1, we need to split the remaining share between R and S.
The total parts of the ratio = \( 4 + 1 = 5 \).
Thus, the share for R is:
\[
\frac{4}{5} \times \frac{4}{5} = \frac{16}{25}
\]
The share for S is:
\[
\frac{1}{5} \times \frac{4}{5} = \frac{4}{25}
\]
Therefore, the new ratio of R, S, and T is:
\[
R : S : T = \frac{16}{25} : \frac{4}{25} : \frac{1}{5} = 16 : 4 : 5
\]
Thus, the new profit-sharing ratio is 16:4:5.