In my above reply, u can substitute 10 by some c and u will get the answer to ur problem.

Look at this....

This is the logic..

((10+a)*b) -((10+b)*a)=10b+ab-10a-ab = 10(b-a)

It depends on whther you opt for intensive study or extensive study. If u r doin intensive study by goin into the subtleties of each topic, one subject per day. If ur study pattern is based on reviewing what was done in class or finished previously by u that involves much to remember, more than one subject per day!!

All the best!!!

It is useful if we remember results of some problems which may serve as a basic building block for a complex problem. Remembering some limits really helped in one of my tests. And it is important that v read the question paper thoroughly before beginning to answer. It helps us to plan to utilize our time effectively.