I have no understanding on how to do these

Ihave this math question 2/3 ÷2 1/10=

One expression below in undefined, and the other expression has a well defined value. which expression is undefined and explain why it has no value. which expression is defined? what is the value of that expression and how do you know? what is a different expression using a trig inverse function that is also undefined?

You are measuring the dimensions of the floor in your bedroom because you are planning to buy new carpet. which unit of measure is the most appropriate to use in this situation?