Instant Review of Needed Prerequisites.
Instead of clearing the fractions (the standard strategy, requiring no "cross multiplication") the student below begins by "collecting fractions." Nevertheless, when a mistake occurs, xyAlgebra reviews the cross multiplication procedure appropriate at THAT step of THAT method , and then offers practice on a similar step.
See also the xyAlgebra Demo program for several dynamic examples.

A. After two correct but unexpected steps, the student multiplies incorrectly, perhaps thinking
that the dot implies parentheses. xyAlgebra notes the error. (Please scroll down to B. below.)

B. xyAlgebra generates a similar step in a "Practicing..." window, below, and reviews the appropriate
prerequisite, like an instructor saying, "Here's how we do that." (Please scroll down to C. below.)

C. Then xyAlgebra implicitly says, "Now you try one," and repeats until the student enters
an acceptable step. Then the subwindow closes and the student resumes the original problem.

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