Question

devon studied the composite figure. he believed the surface area, in square units, could be found by simplifying the expression ( 2((9)(20)) + 2((9)(34)) + (34)(20) + 2(\frac{1}{2}(20)(24)) + 2(\frac{1}{2}(34)(26)) ). what error did devon make? he included the 34 by 20 base of the figure. he used 26 instead of 24 as the slant height of one set of lateral faces. he believed the upper part of the figure was a pyramid instead of a prism. he omitted the rectangle where the upper and lower solids join together.

Explanation:

When calculating the surface area of a composite figure, we need to consider only the outer - facing surfaces. The \(34\times20\) base is internal (where the two solids are joined) and should not be included in the surface - area calculation.

Answer:

He included the \(34\) by \(20\) base of the figure.