Can someone help explain this problem and how to get the correct answer please. It is from the Manhattan gmat site and i don't fully understand their explanation. When a cylindrical tank is filled with water at a rate of 22 cubic meters per hour, the level of water in the tank rises at a rate of 0.7 meters per hour. Which of the following best approximates the radius of the tank in meters? A. √10/2 B. √10 C. 4 D. 5 E. 10 Correct answer is B. Thank you!

Fdelpesce wrote:Can someone help explain this problem and how to get the correct answer please. It is from the Manhattan gmat site and i don't fully understand their explanation. When a cylindrical tank is filled with water at a rate of 22 cubic meters per hour, the level of water in the tank rises at a rate of 0.7 meters per hour. Which of the following best approximates the radius of the tank in meters? A. √10/2 B. √10 C. 4 D. 5 E. 10 In the course of an hour: The VOLUME increases by 22 cubic meters. The HEIGHT increases by .7 meters. Thus: V = 22 when h = .7. Since V = �r²h and � ≈ 3, we get: 22 = �r²(.7) 22 = (3)r²(.7) r² = 22/2.1 r² ≈ 10 r ≈ √10. The correct answer is B.

How do you transition from 22 = (3)r²(.7) to r² = 22/2.1? Don't you have to divide by r² since they are all multiplied together? Which would give you 22/r² on the left side. I get confused between subtracting and dividing to get the figure on the opposite side of the equation because I thought when there is multiplication involved you divide and when its addition/subtraction you either add or subtract? Very much appreciated GMATGuru!

Fdelpesce wrote:How do you transition from 22 = (3)r²(.7) to r² = 22/2.1? Don't you have to divide by r² since they are all multiplied together? Which would give you 22/r² on the left side. I get confused between subtracting and dividing to get the figure on the opposite side of the equation because I thought when there is multiplication involved you divide and when its addition/subtraction you either add or subtract? Very much appreciated GMATGuru! Step by step: 22 = (3)r²(.7) 22 = (2.1)r² Multiply (3)(.7) = 2.1. 22/(2.1) = r² Divide each side by 2.1. 220/21 = r² To clear the decimal, multiply 22/(2.1) * 10/10 = 220/21. 10 ≈ r² Approximate that 220/21 ≈ 10. √10 = √r² Take the square root of both sides. √10 = r. Simplify the righthand side.

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