What is 5/8 divided by 2/1

If you mean 5/8 divided by 2, the answer is 5/16.

If you mean 5/8 divided by 1/2, then it means 5/8 times 2, the answer is 10/8=5/4

A fraction divided to another fraction is equal to the fraction in the numerator multiplied to the reciprocal of the fraction in the denominator. In this case, the product is equal to 5/8 * (1/2) equal to 5/16. This cannot be reduced into lowest terms anymore.