Let A=\1,2,3, ,10\ and B= \ mn:m,n A, m<n and (m,n)=1 \. Then n(B) is equal to :
- 29
- 31
- 37
- 36
Answer
(2) 31
Solution
A fraction in lowest terms with denominator n has (n) choices of m; all such fractions are different.
n(B)= n=210 (n)
=1+2+2+4+2+6+4+6+4=31
Answer: (2)