Calculate the open economy multiplier with proportion of taxes, T = tY, instead of lump-sum taxes as assumed in the text.
Y = C + c (1 - t) Y + l + G + X - M - mY
Y - c (1 - t) + mY = C + l + G + X - M
Y [1 - c (1 - t) + m] = C + l + G + X - M
Y = C+l+G+X−M[1−c(1−t)+m]
Autonomous Expenditure (A) = C + l + G + X - M
∴ Open economy multiplier with proportional taxes:
ΔYΔA=11−c(1−t)+m