A salesperson's ratio of successful signups to the number of people called is 0.275 . this month, the salesperson had 55 signups. how many people did the salesperson call this month?

The main part for understanding this problem lies in the fact that the ratio has been expressed in decimal form. Once that mystery is solved, the problem becomes easy.
Ratio of the successful signups to the number of people attending = 275:1000
The number of people that the sales person successfully signed up = 55
Let us assume the common ratio to be = x
Then
275x = 55
x = 55/275
   = 0.2
then
The number of people that the sales
person called up this week = 1000 * 0.2
                                             = 200
 So the number of people that the sales person called this week is 200. I hope the procedure is simple enough for you to understand.