the sum of a number and its reciprocal is 5/2

the sum of a number and its reciprocal is 5/2

The phrase a number means an arbitrary variable, let's call it x.
The reciprocal of the number means 1/x.

The sum means we add them:
x + 1/x

The word is means an equation, so we set x + 1/x equal to 52
x + 1/x = 52