Bheja fry question

 This bheja fry question I heard it recently on web radio.

Question 

A mobile phone and it's protective case together cost  Rs 110.  Mobile itself is 100 Rs more than its case.  What is the actual value of the mobile phone and its case ???

Answer 

When looking at the first glance, we tend to answer mobile phone is Rs 100 and case Rs 10. 

I thought like that  !!!!

But is it the real answer  ???

If it is, why it would be called bheja fry question  ???!!!

Let us solve it in the methodological way. 

Let the price of the case be X. 

Then as the mobile phone costs 100 more than its case. 

Price of mobile phone is X  +   100

As it is given, both of them together cost Rs 110.

==>>     X   +   X  +  100  =   110

==>>      2X   +    100   =   110

==>>        2X    =   10    (  110  -  100  =  10 )

==>>        X    =   5

Cost of  Protective case of the phone  is     X   is    Rs  5

Cost of mobile phone  =   X  +  100   =  5  +  100  = 105 Rs