Question

Lucila come muchas papas fritas y se preocupa ____ que tita por comer frutas. ?son ____ diferentes! pero se llevan (they get along) bien.

Answer 1

If we use the comparative form, the sentences should be complete in the following way: 

Lucila come muchas papas fritas y se preocupa MENOS que Tita por comer frutas. Son *TAN/ MUY diferentes! pero se llevan bien.

Both terms are acceptable here. Depending on the speaker´s intentions and choices. 

Answer 2

Lucila come muchas papas fritas y se preocupa menos que Tita por comer frutas. ¡Son tan diferentes! pero se llevan bien.

The translation of this statement is as follows:

Lucila eats a lot of fries and worries less than Tita for eating fruits. They are so different! but they get along well.

So in this problem we are using two words: menos and tan that are translated as less and so, respectively. These words have the same meaning as in English. Finally, it is important to point out that the word menos before the conjunction que means less than in English.