Expression is a mathematical phrase which combines, numbers, variables and operators to show the value of something. An equation is a mathematical statement wherein two expressions are set equal to each other. What is it? A sentence fragment, that stands for a single numerical value.
If this fraction is closer to one it will be close to 16/16. And since 8 is half of 16, any fraction that is around 8/16 is closer to 1/2. 15 is closer 16 so this fraction is closer to one.