Let A ={1,2,3, …, 10} and B ={m/n: m, n ∈ A, m < n. and. gcd ( m, n )=1}. Then n ( B ) is equal to:

Let $\displaystyle \mathrm{A}=\{1,2,3, \ldots, 10\}$ and $\displaystyle \mathrm{B}=\left\{\frac{\mathrm{m}}{\mathrm{n}}: \mathrm{m}, \mathrm{n} \in \mathrm{A}, \mathrm{m}<\mathrm{n}\right.$ and $\displaystyle \left.\operatorname{gcd}(\mathrm{m}, \mathrm{n})=1\right\}$. Then $\displaystyle \mathrm{n}(\mathrm{B})$ is equal to :