TIME AND WORK IMPORTANT QUESTION WITH A LOGICAL THINKING TRICK

Today i want to discuss a very important question asked in many exams SSC CGL/BANK PO/ AFACAT /MBA solution of this question is given by very long method in many books 

Two typists of varying skills can do a typing job in 6 minutes if they work together. If the first typist typed alone 4 minutes and then the second typist typed alone for 6 minutes, they would be left with 1/5 of the whole work. How many minutes would it take the slower typist to complete the typing job working alone?

now think logically they both can complete the work in 6 minutes now the first typist typed alone 4 minutes and then the second typist typed alone for 6 minutes, it means if first typist work 2 more minutes after 4 minutes the work will be completed it means he can do 1/5th of work in 2 minutes so whole work in 5 * 2 = 10 minutes it means first can do the work alone in 10 minutes and together it is given in the question they complete the work in 6 minutes so you can easily calculate by basics of time & work that he will complete a work alone in 15 minutes. i.e. our answer that slower typist can complete the work in 15 minutes.