A computer company operating retail stores in six cities in Nigeria invoices goods to the branches at cost plus a mark-up of 25%. What is the mark-up percentage on the selling price?

20%
Explanation:
To calculate the mark-up percentage on selling price, use the formula: Mark-up % on selling price = (Mark-up % on cost ÷ (1 + Mark-up % on cost)) × 100. Here, 25% ÷ (1 + 25%) = 20%.