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n April 13, 1992 the headline of The Chicago Tribune read, “Flood Cripples Loop Businesses.” Workers driving pilings around a bridge had ruptured an abandoned freight tunnel under the Chicago River. Water was gushing into the 40 miles of open tunnels below the 12 square blocks of Chicago’s downtown area called the Loop. The rapidly rising water entered basements, saturated founda- tions, and quickly forced the shutdown of most utilities. Some subway lines were closed, and eventually thousands of workers were evacuated. While divers were used to survey the problem, the Army Corps of Engineers was called in. Their solution was to seal off the portion of the tunnel that was ruptured, using a steel-reinforced concrete plug. Once the plug was in place, the engineers worked on reversing the flow of the water. For over a month, millions of gallons of water were drained off to a water reclamation plant, and the Loop slowly returned to normal. In this chapter we will study algebraic equations and formulas. In Exercises 85 and 86 of Section 2.2 you will see how the engineers used very simple algebraic formulas to calculate the amount of force the water would have on the plug and how much force the concrete plug would withstand. The story of the Chicago flood is just one example of how algebraic formulas are used daily in practical situations. O C H A P T E R 2 Linear Equations and Inequalities in One Variable
