Materials A, B, and C have R values of 1, 4, and 8 ft2-°F-hr/Btu, respectively. If the rate of heat transfer through material A alone is 20 Btu/hr, then the rate of heat transfer through the combination of A, B and C is _____
a. 1.5 b. 2.5 c. 4.0 d. 7.0 e. 80 Btu/hr
a
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