Kenneth Rosen Edition 6th Exercise 1.1 Question 21 (Page No. 19)

Question

Write each of these propositions in the form “p if and
only if q” in English.
a) If it is hot outside you buy an ice cream cone, and if
you buy an ice cream cone it is hot outside.
e) The trains run late on exactly those days when I take it.

In (a) the statement is in the form  “if p then q, and conversely”  and so, the answer should be :-
 " it is hot outside  if and only if You buy an ice cream cone"
But the answer given is  "You buy an ice cream cone if and only if it is hot outside." 
Its also given that The order doesn't matter, Does it really?

In (e) The word  " exactly " how this statement is represented in the form "The trains run late if and only if I take it."
does exactly means if and only if ?
  

Reference:-
 in t

Comments

a) is biimplication

$p\leftrightarrow q$ i.e. $p\rightarrow q$ and $q\rightarrow p$

So, order really not a matter here

e)yes that means p is necessary for q, but sufficient is not needed there

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@ srestha,

 as per your statement, " if p is necessary for q but not sufficient " means only " q->p but not p->q "

but you answered it as yes