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Estimate the surface area of the lake
 

What's the area?

A certain lake has an irregular shape. In order to estimate the area, the North-South distance across the lake is measured every 100 feet down an East-West line. The results are shown in the table below. Use an appropriate technique to estimate the number of acres that the lake covers. Give a complete explanation of how you computed the area.
East-West position (ft) Distance across lake (ft)
0 900
100 1500
200 1800
300 2000
400 2500
500 2700
600 2700
700 2700
800 2700
900 2700
1000 2700
1100 2700
1200 2700
1300 2700
1400 2600
1500 2600
1600 2600
1700 2600
1800 2600
1900 2600
2000 2500
2100 2500
2200 2500
2300 2500
2400 2500
2500 2500
2600 2400
2700 2300
2800 2300
2900 1800
3000 1600
3100 1500
3200 1400
3300 1400
3400 1300
3500 1300
3600 1100
3700 800
3800 0



Problem Moderated by: MrT

 
 
 
 

Problem Solution

There are multiple ways one might attempt the problem. We could do a Riemann Sum, use the Trapezoidal Rule, or use Simpson's Rule. Since a typical lake would be curved, it suggests that Simpson's Rule might be the most appropriate method, although all three methods end up giving basically the same result.

Using Simpson's Rule, one would add the first distance (900), plus four times the second distance (1500), plus twice the third (1800), plus four times the fourth (2000), and so forth, alternating back and forth between two times and four times. We end with four times the next to last number (800) plus the last number (0). The entire sum is then multiplied by (1/3) and by 100 (the width of the interval), to arrive at an estimate of 8,250,000 square feet. Dividing by 43,560 square feet per acre gives a result of 189.39 acres, or 189 acres.

Using the Trapezoidal Rule gives an almost identical answer of 189.05 acres. Using rectangles, and doing a Riemann sum also gives a comparable answer.

2006 Archive

 
 
 



 
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