Write an expression for the amount of water, in liters, in the swimming pool after m minutes. To evaluate an expression at some number means we replace a variable in an expression with the number, and simplify the expression. An equation is a statement that two numbers or expressions are equal. Equations are useful for relating variables and numbers. Many word problems can easily be written down as equations with a little practice.
Many simple rules exist for simplifying equations.
My age in years y plus 20 is equal to four times my age, minus 10. When an equation has a variable, the solution to the equation is the number that makes the equation true when we replace the variable with its value. To find a solution for an equation, we can use the basic rules of simplifying equations. You may evaluate any parentheses, exponents, multiplications, divisions, additions, and subtractions in the usual order of operations. When evaluating expressions, be careful to use the associative and distributive properties properly.