lens maker formula

if u r in xii , giving one hr is not enough...still go chapterwise...suppose take one chapter. learn the concept till half an hr, then next half an hr write what ever u have learnt. while writing u ll get confused at different points. so clear ur doubts at the same time.

next day before going further in the chapter first recall wha u have learnt...then do the same.

this is the best way.