Then do them again. Do the ones that weren't assigned. Generate lots of paper for the recycle bins. Problems ask you to use the material in ways other that the text or lecture can do. Problems give you the opportunity to discover which concepts and ideas are clear and unclear.
Problems can be fun.
Study by working the problems, NOT only by reading your notes and the text. Your best measure of your facility with the material is whether you can work problems. Working problems is essential to success. Work some more problems. More Survival Tips Keep Up Falling behind is death.