A student prepared a solution by dissolving 20 g of common salt in 180 g of water. Calculate the mass by mass percentage of the solution.

Given: 

Mass of solute (common salt) = 20 g 

Mass of solvent (water) = 180 g 

Mass of solution = Mass of solute + Mass of solvent 

Mass of solution = 20 g + 180 g = 200 g 

Mass by mass percentage of solution = (Mass of solute / Mass of solution) × 100 

Mass by mass percentage = (20 g / 200 g) × 100 

Mass by mass percentage = (1/10) × 100 = 10% 

Therefore, the mass by mass percentage of the solution is 10%.