Word QUESTION has 8 letters so total number of word can be formed are 8! For exactly two letters between Q and S Q_ _S_ _ _ _ , _ Q_ _S_ _ _, _ _ Q_ _S_ _ , _ _ _Q_ _S _, _ _ _ _Q_ _S And similarly other 5 will be formed by interchanging Q and S so total favourable outcomes=5*2*6! Probability =5*2!*6!/8!=5/28