document.write( "Question 1092255: You measure the shadow cast by a certain tall building and find that it is 90 feet long. Then you measure the shadow cast by a three-foot post and find it to be 4 inches long. Determine the building's height. \r
\n" ); document.write( "\n" ); document.write( "I wrote it as x/90= 3/4 so 4x=90(3) but my answer was wrong. X= 67.5 (or 68) \n" ); document.write( "

Algebra.Com's Answer #706892 by greenestamps(13200) $\"\"$ $\"About$

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As the second tutor said, your method was fine except that you didn't use compatible units.

\n" ); document.write( "Your formal method uses a proportion, saying that the ratio of the building's height to the length of its shadow is the same as the ratio of the post's height to the length of its shadow. You just overlooked the fact that for the post the given information had the height in feet and the length of the shadow in inches.

\n" ); document.write( "I would encourage you not to be a slave to the formal process of setting up and solving a proportion. In fact, the mistake you made was probably because you just looked at the numbers and set up the proportion, without paying attention.

\n" ); document.write( "Instead, think about the actual physical problem; you will be less likely to make the kind of mistake you made. You have a post that is 3 feet tall and casts a shadow 4 inches long. 3 feet is 36 inches; 36 inches is 9 times 4 inches; so the height of the post is 9 times the length of its shadow.

\n" ); document.write( "But that means the height of the building will be 9 times the length of its shadow. 9 times 90 feet is 810 feet. \n" ); document.write( "

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