On the surface area formula of cylinder To make a cylindrical oil barrel with iron sheet [no cover], the radius of the bottom area is 6 decimeters and the height is 18 decimeters. How many square decimeters of iron sheet is required to make 10 such oil barrels at least [joint is not included]

Make a bottom area of Pai * 6 ^ 2 = 36pai and a circumference area of 2 * 6 * Pai * 18 = 216pai
To make an oil barrel, the iron sheet should be at least 36pai + 216pai = 252pai
Ten such barrels need at least 10 * 252pai = 2520pai
Pai=3.14.
2520 * 3.1415926 = 7916.8m2

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