## Key Concepts

• A linear equation can be used to solve for an unknown in a number problem.
• Applications can be written as mathematical problems by identifying known quantities and assigning a variable to unknown quantities.
• There are many known formulas that can be used to solve applications. Distance problems, for example, are solved using the $d=rt$ formula.
• Many geometry problems are solved using the perimeter formula $P=2L+2W$, the area formula $A=LW$, or the volume formula $V=LWH$.

## Glossary

area
in square units, the area formula used in this section is used to find the area of any two-dimensional rectangular region: $A=LW$
perimeter
in linear units, the perimeter formula is used to find the linear measurement, or outside length and width, around a two-dimensional regular object; for a rectangle: $P=2L+2W$
volume
in cubic units, the volume measurement includes length, width, and depth: $V=LWH$

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