The pressure exerted by a certain liquid at a given point varies directly as the depth of the point beneath the surface of the liquid.

Question

The pressure exerted by a certain liquid at a given point varies directly as the depth of the point beneath the surface of the liquid. The pressure at 50 feet is 21 pounds per square inch. What is the pressure at 190 feet?

Answer 1

This is a proportion problem. You have to set up the equation like this:

 

     50 feet      = 190 feet

 21 lb/sq. in.          x

 

So that the related terms (the amount of feet and the corresponding pressure) are on the same side of the equals sign, and so that the same units are on the top/bottom (in this case, feet are on the top and lb/sq. in. is on the bottom)

 

Then cross multiply:

 

(50 feet)x = (21 lb/sq. in.)(190 feet)

 

and solve for x:

 

50x = 3990

x = 79.8

 

So at 190 feet, the pressure is 79.8 lb/sq. in.

Answer 2

Sarah, this is a ratio problem.  So, we have 50/21 = 190/x.  Can you solve for x?