# Exam Study Guide: Filtration Rate Math Question

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When faced with a licensing exam, don't struggle with test anxiety! Use the question below and others from our Exam Study Guide series to study and prepare for exam questions. Take a look at this sample water treatment licensing question along with an explanation of the correct answer.

Sample question:

An operator closes the influent valve on a gravity filter and notices the water level drops eight inches in two minutes. What is the filtration rate in gpm/ft2 of surface area?

A) 0.67 gmp/ft2

B) 5.0 gmt/ft2

C)10 gpm/ft2

D) 2.5 gpm/ft2

The correct answer is D, 2.5 gpm/ft2 because 8 ÷ 12 = 0.67'; 0.67' x 1' x 1' x 7.48 gallons = 5.0 gallons; 5.0 gallons ÷ 2 minutes = 2.5 gpm; 2.5 gpm ÷ 1ft2 = 2.5 gpm/ft2.

About the author: Drew Hoelscher is the program director of drinking water operations at the Environmental Resources Training Center (ERTC) in Edwardsville, Illinois.

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