Placement of parentheses is paramount. Scholars adjust the location of parentheses in a numerical expression so its value matches a given value. A slider interactive helps with this task.

We'd all love to have barrels of candy. An interactive shows the steps in evaluating a numerical expression that reflects the cost of buying several different barrels of candy.

An interactive challenges mathematicians to add mixed fractions with unlike denominators. Five questions—fill-in-the-blank and multiple-choice—build from one to the next leading the way to an open discussion about denominators and...