Write an expression for the distance the car will have traveled after h hours. Water is filling the pool at the rate of 100 liters per minute. 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.