Hello,
I can offer you only the original string in German because of the setup of my survey.

"In dieser Umfrage sind 18 Fragen enthalten."

In translation it would be something like this: "This survey includes 18 questions."

If the survey has filters (if clauses) there are not 18 questions for all users. Some of them might see less of 18.

The users should know the minimum and maximum number of questions.

"This survey includes <min> to <max> questions."

As an alternative, if you don't like to expose the <min> value, try this: "This survey includes up to <max> questions."

Regards,
Christian