please solve this forex's question:-

Rs./pound  75.31/75.33

pound/dollar  .6391/.6398

dollar/yen  .01048/.01052

The rate at which yen can be purchased will be?

I took coaching from Rajesh Makkar sir...his approach for this type of ques is to multiply down .i.e.

Rs./yen=75.31*.6391*.01048/75.33*.6398*.01052

one of my frnd is studying from rajiv singh sir's cd..according to rajiv singh sir this short cut method should not be followed in exams..so guys pls tell me that rajesh makkar sir's approach is right or wrong???