Blended learning systems combine face-to-face instruction with distributed learning systems. We designed a blended course in physics courses and conducted it for from lower- to upper-level classes since 2015. We used online homework to enhance study time outside class, and found that students spent about 100~160 minutes per week on homework in all classes. In a face-to-face class, collaborative group activities were conducted in which students share what they have learned and what they have deduced the general strategy applicable to other problems from the online homework. After these activities, students are finally given short writing activities to explain their problem solving strategy.
