A test has twenty questions worth 100 marks in total. There are two types of questions. Multiple choice questions are worth 3 marks each and essay questions are worth 11 marks each. How many multiple choice questions does the exam have?

Let $m$ be the number of multiple choice questions and $e$ be the number of essay questions.

From the problem statement:

1. Total questions:

   $$m + e = 20 \implies e = 20 - m$$

2. Total marks:

   $$3m + 11e = 100$$

Substitute $e = 20 - m$ into the marks equation:

So, there are 15 multiple choice questions (and $e = 5$ essay questions).

Therefore, (B) is the correct option.