Consider a 2.55 m by 10.0 m housing wall, with a section shown in the diagram.
A builder has the choice of using 1.5 in. by 3.5 in. studs (at $2.25 each, with R-value R=5),
or 1.5 in. by 5.5 in. studs (at $4.20 each; R=8). The studs are spaced with a center-to-center distance of 40 cm.
The wall with the thinner studs can accommodate R=8 insulation (at $3.40 per m2), whereas the thicker wall can accommodate R=23 insulation (at $6.55 per m2).
Assume that the house is to be built in an area where the average difference between the inside and the outside temperature is 7.5 °C. If the cost of

Question

Consider a 2.55 m by 10.0 m housing wall, with a section shown in the diagram.
A builder has the choice of using 1.5 in. by 3.5 in. studs (at $2.25 each, with R-value R=5),
or 1.5 in. by 5.5 in. studs (at $4.20 each; R=8). The studs are spaced with a center-to-center distance of 40 cm. 
The wall with the thinner studs can accommodate R=8 insulation (at $3.40 per m2), whereas the thicker wall can accommodate R=23 insulation (at $6.55 per m2). 
Assume that the house is to be built in an area where the average difference between the inside and the outside temperature is 7.5 °C. If the cost of

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