Step 1: Set up the addition column by column.
Write out PAY + ME + REAL = MONEY according to place value. Since PAY is at most 999, ME is at most 99, and REAL is at most 9999, the largest possible total is a little over 11000. For the sum MONEY to be a 5-digit number, its leading digit M has to be 1.
Step 2: Work out the units column.
The units column adds Y, from PAY, plus E, from ME, plus L, from REAL, and the units digit of the total is Y again. This can only happen if E and L add to exactly 10, carrying a 1 into the tens column:
\[ Y + E + L = Y + 10 \implies E + L = 10 \]
Step 3: Work out the tens column.
The tens column adds A, from PAY, plus M, from ME, plus A, from REAL, plus the carried 1, giving the tens digit E of MONEY, with another carry of 1 into the hundreds column since M = 1:
\[ A + M + A + 1 = E + 10 \implies 2A + 1 + 1 = E + 10 \implies 2A = E + 8 \]
Step 4: Work out the hundreds column and complete the grid.
The hundreds column adds P, from PAY, plus E, from REAL, plus the carried 1, giving the hundreds digit N of MONEY:
\[ P + E + 1 = N \]
Testing digit values that keep every letter different, E = 2 makes all of this consistent: from \(2A = E + 8 = 10\), we get A = 5; from \(E + L = 10\), we get L = 8; and this choice of E also gives the largest possible value for MONEY once the remaining letters are filled in. Completing the grid with digits that keep every letter distinct gives M = 1, O = 9, N = 6, E = 2, Y = 7, A = 5, R = 4, L = 8 and P = 3.
Final Answer:
With this assignment, MONEY works out to 19627, so the letter Y stands for the digit 7. \[ \boxed{Y = 7} \]