Present Height plus decreased height equal to original height. \ \

\

The equation represents the situation is, 450 + d = 481 \ \

Subtraction property of equality: if a = b, then .

              (Subtract 450 from each side).

                                     (Additive inverse property:)

                                                 (Add:)

Check:

To check the solution, substitute in original equation.  

                                         (Add: )

Compare the values, the equation is true. The solution is .

Decrease in the height of the pyramid is 31 ft.