
Chapter 7: Other aspects of capital investment appraisal
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The final solution and its interpretation: dual prices or shadow prices
Variable in the
solution
x
y
z
Y
0
Y
1
U
x
U
y
U
z
Total
(million)
Project Z (z)
0
2
5
1
0
- 6
0
0 0.2
Y
1
0
1
2
0
1
- 3
0
0 1.6
Project X (x)
1
0
0
0
0
1
0
0 1.0
Project Y (y)
0
1
0
0
0
0
1
0 1.0
U
z
0
0
1
0
0
0
0
1 0.8
Objective function
0
0
0
0.6
0
1.6
0.8
0 6.4
The final tableau is shown here, with the solution that maximises total NPV. The
problem in this example is fairly simple, so the solution is quite straightforward.
To maximise total NPV, the company should invest in 100% of Project X, 100% of
Project Y and 20% of Project Z (since x = 1.0, y = 1.0 and z = 0.2). This will leave
unused capital of $1.6 million in Year 1 (since Y
1
= 1.6). The proportion of Project Z
not invested in is 0.8.
Total NPV will be $6.4 million.
The solution also shows the dual prices or shadow prices of the variables that are
not in the solution. These are Y
0
, U
x
and U
y
.
All the available capital in Year 0 is used up by the solution. The dual price
indicates that if $1 of extra capital could be made available in Year 0, the total
NPV could be increased by $0.4.
The maximum investment is made in project X, so U
x
= 0 in the final solution.
The dual price for U
x
indicates that if the maximum investment in project X
could exceed 100%, the total NPV could be increased by $1.6 million for every
additional project X that is available.
The maximum investment is made in project Y, so U
y
= 0 in the final solution.
The dual price for U
y
indicates that if the maximum investment in project Y
could exceed 100%, the total NPV could be increased by $0.8 million for every
additional project Y that is available.
Dual prices for projects are not particularly significant. However,
the dual price or
shadow price for capital is significant
. It shows by how much total NPV could be
increased if more capital could be made available in that year (given no change in
any other constraint in the problem).
For example, this solution indicates that if the available capital in Year 0 could be
increased by, say, $1 million, from $9 million to $10 million, there would be a
different optimal solution and the total NPV for this solution would be higher by
$400,000 ($1 million × 0.4).