To calculate the goodwill of the firm on Sanju’s admission, follow these steps:
Step 1: Calculate the total capital of the firm based on Sanju’s share.
Sanju's share in the profits is $\frac{1}{5}$. This means the total capital of the firm can be calculated as:
\[
\text{Total Capital of the Firm} = \frac{\text{Sanju’s Capital}}{\text{Sanju’s Share}} = \frac{₹1,00,000}{\frac{1}{5}} = ₹5,00,000.
\]
Step 2: Calculate the combined capital of existing partners.
The combined capital of Manas and Ranvir is:
\[
\text{Combined Capital} = ₹1,20,000 + ₹80,000 = ₹2,00,000.
\]
Step 3: Calculate the goodwill of the firm.}
Goodwill of the firm is the difference between the total capital of the firm and the combined capital of the existing partners:
\[
\text{Goodwill} = \text{Total Capital of the Firm} - \text{Combined Capital of Existing Partners}.
\]
\[
\text{Goodwill} = ₹5,00,000 - ₹2,00,000 = ₹3,00,000.
\]
Final Answer:
The goodwill of the firm on Sanju’s admission is \( \boxed{₹2,00,000} \).