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Explanation:
psi = pounds per square inch
1 foot = 12 inches
1 square foot = 144 square inches
I squared both sides to get the second equation. Think of a 12 by 12 square representing 12 inches along each side, so that leads to 12*12 = 144 square inches being the same as 1 square foot.
That last equation helps us convert from square inches to square feet like so:
[tex]20 \text{ psi} = \frac{20 \text{ pounds}}{1 \text{ square inch}}\\\\20 \text{ psi} = \frac{20 \text{ pounds}}{1 \text{ square inch}}*\frac{144 \text{ square inches}}{1 \text{ square foot}}\\\\20 \text{ psi} = \frac{20*144}{1*1}*\frac{\text{ pounds}}{\text{ square foot}}\\\\20 \text{ psi} = \frac{2880 \text{ pounds}}{1 \text{ square foot}}\\\\20 \text{ psi} = 2880 \frac{\text{ pounds}}{\text{ square foot}}\\\\20 \text{ psi} = 2880 \text{ pounds per square foot}\\\\[/tex]
Notice in the jump from the second step to the third step, we have the "square inches" unit cancel out when dividing. All that's left is "pounds" up top and "square foot" down below.
In short, we simply multiply by 144 to go from 20 to 2880.
