## 38 - 40 Solved problems in maxima and minima

**Problem 38**

A cylindrical glass jar has a plastic top. If the plastic is half as expensive as glass, per unit area, find the most economical proportion of the jar.

**Problem 39**

A trapezoidal gutter is to be made from a strip of tin by bending up the edges. If the cross-section has the form shown in Fig. 38, what width across the top gives maximum carrying capacity?

**Problem 40**

Solve Ex. 39, if the strip is 11 inches wide and the base is 7 inches wide.

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