
Illustration 69
Presume the consumption and investment functions are as below:
C = 100 + 0.75 (Y – 0.45Y)
I = 400 – 4r
G = 200
- Find the Equation of the IS Curve and
- Find the Equation of the IS Curve when government outlay enhances by $ 80.
Solution
- Equation of the IS Curve
Y = C + I + G
Y = 100 + 0.75 (Y – 0.45Y) + 400 – 4r + 200
Y = 700 + 0.75(0.55Y) – 4r
= 700 – 4r + 0.41Y
Y – 0.41Y = 700 – 4r
0.59Y = 700 – 4r
Y = 700 – 4r
0.59
Y = 1,186 – 6.8r
- Equation of the IS curve when government outlay enhances by $ 80,
Y = C + I + G
Y = 100 + 0.75(Y – 0.45Y) + 400 – 4r + 280
Y = 780 – 4r + 0.75(0.55Y)
= 780
+ 0.41Y – 4r
Y – 0.41Y = 780 – 4r
Y = 780 – 4r
0.41
Y = 1902 – 9.8r
Illustration 70
Presume the consumption and investment functions and the government outlay are as below:
C = 100 + 0.6 (Y – 40)
I = 300 – 20r
G = $ 240 millions
Suppose that the money supply is $ 392 millions, the money demand function is md = 0.5Y – 12r
- Determine the Equation of the IS Curve
- Determine the Symmetry of the LM curve
- Determine the Concurrent Symmetry for the IS and LM curves
- Determine the Concurrent Symmetry for the IS and LM curves when government outlay enhances by $ 110 millions.
Solution
(1) Equation of the IS Curve
Y = C + I + G
Y = 100 + 0.6 (Y – 40) + 300 – 20r + 240
Y = 740 – 20r + 0.6Y – 24
Y = 716 – 20r + 0.6Y
Y – 0.6Y = 716 – 20r
0.4Y = 716 – 20r
Y = 716 – 20r
0.4
Y = 1,790 – 50r
(2) Equation of the LM curve md = 0.5Y – 12r
ms = 392
In symmetry, md = ms.
0.5Y – 12r = 392
0.5Y = 392 + 12r
Y = 392
+ 12r
0.5
Y = 784 + 60r
- Concurrent Symmetry for the IS curve and LM curves
IS = LM
1,790 – 50r = 784 + 60r
110r = 1790 – 784
r = 1006 / 110
r = 9.2%
Y = 1790 – 50 * 9.2
Y = 1,330
Concurrent symmetry for the IS curve and LM curve subsists when Y = 1,330 and r = 9.2%.
- Concurrent symmetry for the IS curve and LM curve when government outlay enhances by $ 110 millions.
IS Equation Y = C + I + G
Y = 100 + 0.6 (Y – 40) + 300 – 20r + 350
Y = 750 + 0.6Y – 24 – 20r
Y = 726 + 0.6Y – 20r
Y – 0.6Y = 726 – 20r
0.4Y = 726 – 20r
Y = 726 – 20r
0.4
Y = 1,815 – 50r
LM Equation stays unaffected at
Y = 784 + 60r
Concurrent symmetry for the IS curve and LM curve is as follows:
IS = LM
1,815 – 50r = 784 + 60r
110r = 1,031
r = 1,031 / 110
r = 9.4%
Y = 1,815 – (50 * 9.4)
Y = 1,815 – 470
Y = 1,345
Concurrent symmetry for the IS curve and LM curves subsists when Y = 1,345 and r = 9.4%.
Illustration 71
Suppose that the consumption and investment functions are as below:
C = 100 + 0.4Yd
I = 400 – 4r
G = 260
Ascertain the following:
- The Equation of the IS Curve
- The equation of the IS Curve when the following,
- Government Outlay enhances by $100 millions
- Taxes enhances by $100 millions
- Government Outlay enhances by $100 millions and taxes by $100 millions
- Ascertain the position of the curve
Solution
- Equation of the commodities market symmetry or the IS Curve Y = C+ I + G
Y = 100 + 0.4Yd + 400 – 4r + 260
Y = 760 – 4r + 0.4(Y – 0)
Y = 760 – 4r + 0.4Y
Y – 0.4Y = 760 – 4r
0.6Y = 760 – 4r
Y = 760 – 4r
0.6
Y = 1,267 – 6.7r
- Equation of the IS Curve
- Government Outlay enhances by $100 millions
Y = C
+ I + G
Y = 100
+ 0.4Yd + 400 – 4r + 360
Y = 100 + 0.4 (Y-0) + 400 – 4r + 360
Y = 860 + 0.4Y – 4r
Y – 0.4Y = 860 – 4r
0.6Y = 860 – 4r
Y = 860 – 4r
0.6
Y = 1,433 – 6.7r
- Taxes enhances by $100 millions
Y = C + I + G
Y = 100 + 0.4Yd + 400 – 4r + 260
Y = 100 + 0.4 (Y – 100) + 400 – 4r + 260
Y = 760 – 4r + 0.4Y – 40
= 720 – 4r + 0.4Y
Y – 0.4Y = 720 – 4r
0.6Y = 720 – 4r
Y = 720 – 4r
0.6
Y = 1,200 – 6.7r
- Government outlay enhances by $100 millions and taxes by $100 millions.
This is the case of balanced budget.
Y = C + I + G
Y = 100 + 0.4 (Y – 100) + 400 – 4r + 360
Y = 860 – 4r + 0.4Y – 400
Y = 460 – 4r + 0.4Y
Y – 0.4Y = 460 – 4r
0.6Y = 460 – 4r
Y = 460 – 4r
0.6
Y = 767 – 6.7r
- Position of the curve will contain the following points:
- The nominal IS Curve, Y = 1,267 – 6.7r will be given by the IS1 curve.
- The IS curve when government outlay enhances by $ 100 millions, Y = 1,433 – 6.7r is given by the IS curve IS2. This denotes a horizontal movement of $ 166 millions.
- The IS curve when taxes enhances by $100 millions, Y = 1,200 – 6.7r and is given by the IS3 curve. This denotes a horizontal movement towards left of $ 67 millions from the IS1 curve.
- The IS curve when government outlay enhances by $ 100 millions and taxes by $ 100 millions, Y = 767 – 6.7r is given by the IS4 curve. This denotes a horizontal movement towards the right of $ 100 millions. This is for the reason that ΔG = ΔT = 100 million dollars.
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