In a fraction if you make the bottom part bigger while keeping the top same, the fraction's value shrinks. But if the bottom part gets smaller, the fraction grows.
So, 1/9 and 1/10 are both smaller than 1/8.
As for 3/10, let's change it so that the top number becomes 1. 3/10 = 1/(10/3).
That's approximately 1/3. So, it's not smaller than 1/8.
