I'd like to provide a little insight, having my B.A. in Psychology.
I've taken the professional Myers-Briggs Type Indicator test online. It's a 90-someodd question survey that does, in fact, only give two options to each question, and they determine the direction you sway on the particular spectrum.
Now, there is a big difference in efficacy between the professional test and these free online type surveys. Just remember that these are loose Types, not fixed Traits. The true MBTI has been used for decades and is consistently evaluated on statistical metrics. There is actually even a process following the survey, yet before you receive results) where you are given the descriptions and examples of each spectrum, one by one. After this educational process, you are asked to choose which of the two that YOU believe you fall under, and then it shows what your survey results say and gives a visual indication where you lie on the spectrum (say between Introversion/Extroversion). At the very end, it then allows you to choose which results layout that you want, either the ones you chose for yourself or the results from your survey answers.
The MBTI is meant to be a process in which you are given the survey by a Psychologist licensed to give the test and evaluate its results. This is largely so that they make sure people understand that the results are not definitive of who we are. We constantly move on each of the four spectra (not usually very far) based on experiences and changes in our lives. After significant life events, a person's Type can change drastically (this is especially true when younger than mid-20's).
... I sort of lost my train of thought, and don't want to ramble.
I am an ISTJ.
Strongly Introverted, though I am rarely "drained" by large events with a lot of people, so I use my Extroversion often.
Slight Thinking, I very often am considerate of what others need and am constantly looking for input to ensure I'm not being too task-focused. (I called myself Feeling when I took the MBTI.)
Moderate Judging, though I like to do the "What If's" and think on theory, which are aspects of the Perceiving type.