A word problem is just an equation hiding inside a sentence. The skill is to choose a letter for the unknown number, then write the relationship the words describe. Once it is an equation, you already know how to undo each step to find the answer.

Take the riddle: "I think of a number, multiply it by 3 and add 4 to get 19." Let the number be n. "Multiply by 3" is 3n; "add 4" makes 3n + 4; "to get 19" means it equals 19:

Reading the story phrase by phrase is really just turning words into algebra — and the equals sign is the word that finishes the sentence.

See it built

Watch the words appear, then the equation form underneath them one phrase at a time — and finally get solved.

See it explained

Sal Khan turns word problems into equations and then solves them.