marginal utility of consuming vs marginal rate of substitution good day all

I am taking second year economics, but my textbook is not very clear on this topic

A quoted from 


  Intermediate Microeconomics and Its Application. Nicholson, Snyder. 11th Edition.


Used in question: 2 Extracts from textbook, 1 text and 1 graph:


  Indifference Curve Used as reference:





  Text Extract




Tutorial Question given by university:



My question:

From the extract, I understand that the MRS is determined by the change in hamburgers / change in softdrinks which gives MRS = |2|.

From my tutorial question, slightly different terminology was used ("consumption"), which resulted the answer shown.

I do not understand why the answer for the tutorial question is 1/5 and not 5 (based on the example from the book). 

Help would be very much appreciated!
This is because the question is asking the MRS of soda for hotdogs not the MRS of hotdogs for soda.

i.e 

$MRS(MU(soda),MU(hotdogs))=MU(soda)/MU(hamburgers)= 2/10=1/5$ To get 5 you need to solve the MRS of hotdogs to soda $MRS(MU(hotdogs),MU(soda))=MU(hamburgers)/MU(Soda)=10/2=5$

Hope this helps.