It was about 17.4%
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% error=
actual value-estimated value
Then divide that by actual value
3/5 is greater because the decimal is .6 while 21/40 is .525
Start by adding together the shortest two sides, 7 and 8.7 inches. Result: 15.7 inches. Because this sum is greater than the longest side, 15.4 inches, it's possible to construct a triangle, whose largest angle will be close to 180 degrees.
