Because in '1/8', there are 8 whole number but one shaded and in '1/10', there are 10 whole number and one shaded. as you see in the picture, the smaller the denominator is(when it goes up), the more bigger it is than those below. So 1/8 is greater than 1/10. but 1/8 is smaller than 1/3, because remember:
*The more you go down(or the higher the denominator is), the more you are making the fraction into more smaller pieces.
*The more you go down(or the higher the denominator is), the more you are making the fraction into more smaller pieces.