



 
Hi Sharon, I remember that there are 231 cubic inches in a US gallon so I am going to change your dimensions to inches. Thus your cistern is 12 × 12 = 144 inches deep and has a radius of 5/2 × 12 = 30 inches. The volume of a right circular cylinder is
where r is the radius and h is the height. Thus your cistern has a volume of
Which is
Penny  


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