# SAT problem solving explanation

## Test 11

6. For a wall of a given material and of a fixed surface area, the rate of heat loss by conduction through the wall is inversely proportional to the thickness (T) of the wall, and directly proportional to the temperature difference (d) across the wall. The rate of heat loss could be given by which of the following expressions?

A. 2d/T
B. 2 T/d
C. 2d + ½ T
D. 2(d + ½ T)
E. T/d

Explanation:

Rate (R) is directly proportional to d. We write this as R = k.d, where k is a constant.
Rate is inversely proportional to T. We write this as R = k. 1/T, where k is a constant.
In the combined expression, d must appear in the numerator and T in the denominator. This is the case in A.

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