Lesson 2

Example 2

 

A roofer needs to estimate the number of bundles of shingles he must order to cover the roof in the illustration. A bundle of shingles covers 100 ft2. The roofer knows from experience that he should overestimate by adding another 4% to account for waste, as well as extra shingles needed for the first rows and the ridges, hips, and valleys on the roof. On bare or new roofs, carpenters can use a standard sheet of plywood as their referent. A standard sheet of plywood is a rectangle measuring 4 ft wide and 8 ft long. It covers an area of 4 ft × 8 ft or 32 ft2.

 

The image to the left shows the bare roof with the standard sheets of plywood exposed. The roof is covered by approximately 102 sheets of plywood. How many bundles of shingles will the roofer need to cover the roof in the illustration?

 

 

 

Solution

 

From the ground, the roofer counts the number of sheets of plywood on the roof. His count is approximately 102 sheets.

 

 

To account for waste, as well as the extra amount needed, the roofer adds on 4%.

 

 

 

If each bundle covers approximately 100 ft2, the roofer will order 34 bundles, since 34 × 100 ft2 = 3400 ft2.

 

Self-Check 1

1. Marty works as a groundskeeper at a local golf course. Marty’s supervisor has asked him to apply fertilizer to the green on the twelfth hole. Marty must estimate the area of the green before he applies the fertilizer. He knows the green is almost a perfect circle. Marty also knows that one pace is approximately one yard. How can he estimate the area of the green? Answer
   
   
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