One of the initial questions that arise when first considering teaching in a blended format is what the exact make-up of the course should be; in other words, how much time should be spend in each of the two modes of instruction. The short answer is that there is not a single “right” ratio of face-to-face and online time. Each course is a unique case.
Blended courses show enormous variety in how the face-to-face ratio to online time is distributed. For example, some instructors might choose to replace one class per week with online assignments. Others might meet with their students in class for several weeks and then suspended class meetings for several weeks as the students worked independently or in teams on online assignments. What’s right for your course will be a decision you’ll make after considering your course objectives, and weighing the benefits of each of the instructional modalities for reaching those objectives.
The courses described above, which move some instruction online and have a resulting reduction in the amount of time spend in a face to face classroom setting, follow the “replacement” model: the time previously spent in class has been shifted to online instructional time. It is possible to add online content to a face-to-face course without replacing any classroom time. Consider a situation in which a math instructor provides online practice problems to students, allowing them to work on problems at their convenience. This example could be seen as a “web-enhanced” course, because the online materials are supplemental to the face-to-face instruction. For the most part, blended learning courses aim to replace face-to-face time.
"another test for the lens ... I wonder if the author of this article can read this comment ? :)"