Question: The number of distinct rational numbers x such that  $ 0<x<1 $  and  $ x=\frac{p}{q}, $  where  $ p,q\in {1,2,3,4,5,6}, $  is
Options:
A) 15
B) 13
C) 12
D) 11
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  Answer:
Correct Answer: D
Solution:
- [d] As  $ 0<x<1, $  we have  $ p<q $  The number of rational numbers  $ =5+4+3+2+1=15. $  When p, q have a common factor, we get some rational numbers which are not different from those already counted. There are 4 such numbers:  $ \frac{2}{4},\frac{2}{6},\frac{3}{6},\frac{4}{6} $  Therefore, required number of rational numbers  $ =15-4=11. $