The molarity of a solute in solution is defined to be the number of moles of solute per liter of solution (1 mole = 6.02 × 10²³ molecules). If X is the molarity of a solution of sodium chloride (NaCl), and Y is the molarity of a solution of sodium carbonate (Na₂CO₃), the molarity of sodium ion (Na⁺) in a solution made of equal parts NaCl and Na₂CO₃ is given by M = 0.5X + Y. Assume X and Y are independent and normally distributed, and that X has mean 0.450 and standard deviation 0.050, and Y has mean 0.250 and standard deviation 0.025.

a. What is the distribution of M?

b. Find P(M > 0.5).