$$2/3 - 1/5 + 1/10$$
Here the LCM of $$3, 5$$ and $$10$$ is $$30$$
$$= \left (2 \times 10 \right )/ \left (3 \times 10 \right ) - \left (1 \times 6 \right )/ \left (5 \times 6 \right ) + \left (1 \times 3 \right )/ \left (10 \times 3 \right )$$
By further calculation
$$= 20/30 - 6/30 + 3/30$$
So we get
= $$\left (20 - 6 + 3 \right )/30$$
$$= 17/30$$