Learners follow the steps for adding and subtracting signed numbers and complete practice exercises.

Learners follow step-by-step instructions for finding the lowest common denominator for a group of algebraic fractions and then enter their answers to three problems. Immediate feedback is provided. This activity has audio content.

Learners follow steps to add fractions with different denominators. They also review fraction concepts, do a drag-and-drop exercise involving fraction terms, and add fractions with common denominators.

Students review the spelling rules for adding a suffix to a base word. They practice changing the "y" to "i" for some of the words that end in "y."

In this animated object, learners follow an analogy of water flowing through pipes and valves to see how resistance decreases in a parallel circuit as branches are added.

In this animated object, learners follow an analogy of water flowing through pipes and valves to see how current increases in a parallel circuit as branches are added.

In this learning activity you'll solve three binary subtraction problems using the 2's complement method.

Students view a video that shows the correct methods for starting a GTAW weld pool and adding filler. It focuses on the two problems that many students have – adding filler too soon and angling the torch so that the filler melts prematurely on the filler rod. Note: This activity is 3.6 mb.

Ions are electrically charged particles obtained from an atom or from a chemically bonded group of atoms by adding or removing electrons. Eight examples illustrate the number of protons, neutrons, and electrons in positive ions (cations) and in negative ions (anions).

Students explore the history of U.S. Constitutional amendments and the process involved in adding an amendment. In an interactive exercise, learners author their own amendments and explain why these should be added to the Constitution.

Students practice adding some of the basic prefixes to words in the English language.

Students practice adding prefixes to a variety of words in the English language.