12Compare from left to right. How do we get from 3 to 12? Add 9 or multiply by 4.How do we get from 7 to 28? Multiply by 4.If we multiply 11 by 4, we get 44.The pattern is to multiply our number, n, by 4.The algebraic expression to describe this is:4n
13Describing Unknown Numbers When you don’t know what a number is, let a variable stand for that number.Use an algebraic expression to describe what you’re looking for.
14ExampleWrite an algebraic expression to describe Jerry’s age. Use the following information:Jerry is 4 years younger than his brother Steve.First, we have to know how old Steve is. We do not have an age for Steve, so we will use a variable:Let s = Steve’s age.Now that we have determined Steve’s age (s), we can use it to determine Jerry’s age. Jerry is 4 years younger than Steve.s - 4
15If Steve is 22 years old, then how old is Jerry? Jerry is 18 years old.22 - 418