In the calculation of goodwill for a partnership firm during a change in profit-sharing ratio, the correct method is to use the average profit after accounting for all adjustments, such as partners’ interest on capital. Since the average net profit after interest is ₹12 lakh, goodwill is calculated as ₹12 lakh × 3 years = ₹36 lakh. It is incorrect to add back the interest on capital (₹10 lakh) and use ₹22 lakh × 3, as interest on capital is already appropriated and not part of the residual profit used to value goodwill.