How can expressions be written and evaluated to solve for unknowns in the real world?
Writing expressions requires figuring out which quantity in a situation is unknown, and define a variable to represent that quantitiy.
We look for words in the problem that will help us out what kind of operation to use in a given situation.
Example:
Donna bought 5 chocolate bars, and then ate some. Write an expression to represent how many chocolate bars Donna has left.
If we let the variable c represent the number of chocolates Donna has eaten, then we can write the expression on how many bars Donna has left as: 5 - c
so in terms of x we write