From this link you will get to know about 4.8 rule http://books.google.co.in/books?id=cznaW-8K9iEC&pg=PA24&lpg=PA24&dq=what+is+the+4.8+rule+in+mathematics&source=bl&ots=fnNDIcQlxt&sig=fm4YvLmkgZn7Sg9bXgx0P_4wY98&hl=en&sa=X&ei=MCVxUpu1LMOlrQfFhICAAQ&ved=0CEwQ6AEwAw#v=onepage&q&f=false
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From this link you will get to know about 4.8 rule http://books.google.co.in/books?id=cznaW-8K9iEC&pg=PA24&lpg=PA24&dq=what+is+the+4.8+rule+in+mathematics&source=bl&ots=fnNDIcQlxt&sig=fm4YvLmkgZn7Sg9bXgx0P_4wY98&hl=en&sa=X&ei=MCVxUpu1LMOlrQfFhICAAQ&ved=0CEwQ6AEwAw#v=onepage&q&f=false
from this link you will get to know about 4.8 rule