A person add 1.5 liter water in a solution so that concentrations of HCI in solution becomes 60% from 72% initially. Find the quantity of HCI in solution initially.

Adding water dilutes the HCl concentration from 72% to 60%. Let initial HCl = x liters. Initial solution = x/0.72 (since 72% is HCl). After adding 1.5L: total = x/0.72 + 1.5, and HCl still = x. So x / (x/0.72 + 1.5) = 0.60. Solving: x = 0.60(x/0.72 + 1.5), so x = x/1.2 + 0.9. Then x - x/1.2 = 0.9, so x(1 - 1/1.2) = 0.9, so x(0.2/1.2) = 0.9, so x = 0.9 × 6 = 5.4 liters.