JavaScript; calculate a mean, excluding certain values

My question

I have a series of variables populated by satisfaction scores from a survey. These scores are between 1 and 10, but can also be 99 signifying "I don't know".

Without a series of If statements, is is possible to calculate the mean of all the questions while excluding the 99s?

My attempt

Apologies for the slightly odd way question data is retrieved in my example below. Each of the 3 questions has 3 measures which are given a satisfaction rating. The Confirmit survey platform I'm using uses f('x_y').get() to fetch answers where x = question ID and y = measure so f('q3_1').get() returns the score given to the 1st measure in question 3.

var qList = ['q3', 'q4', 'q6']; // 3 questions, each containing 3 satisfaction scores

var output
var i
for (i = 0; i < qList.length; i++){ // For each question in qList...
    // Collect each satisfaction rating & convert to flaoting-point number:
    var sat1 = parseFloat( f(qList[i].concat('_1')).get() );
    var sat2 = parseFloat( f(qList[i].concat('_2')).get() );
    var sat3 = parseFloat( f(qList[i].concat('_3')).get() );

    // Calculate average satisfaction
    var satAvg = (sat1 + sat2 + sat3) / 3;

    if (satAvg == NaN){
        output = "<em>Did not answer</em>";
    } else {
        output = satAvg.toString().concat('/10');
    }

    // Write to open-text questions:
    f('av'.concat(i +1)).set(output)
}

The contents of the open-text av1, av2 & av3 questions populated by the above are concatenated into an email alert, keeping this alert short is why an average is required. Obviously having any "I don't know" responses is going to affect this mean.

EDIT: Based on @Cimbali's answer below, I'm now putting the values into an array. This means unwanted answers (11 & blanks) can be excluded by a single if statement in a loop:

var qList = ['q3', 'q4', 'q6'];

// Get satisfaction scores:
var i;
for (i = 0; i < qList.length; i++){
    var answers = [
        parseFloat( f(qList[i].concat('_1')).get() ),
        parseFloat( f(qList[i].concat('_2')).get() ),
        parseFloat( f(qList[i].concat('_3')).get() )
    ];

    // Remove "I don't know" (11) and blank answers:
    var y;
    for (y = 0; y < answers.length; y++){
        if ( answers[y] > 10 || isNaN(answers[y]) ){
            answers.splice(y, 1);
        }
    }

    // Calculate sum of remaining answers:
    var sum = 0;
    var x;
    for (x = 0; x < answers.length; x++){
        sum += answers[x];
    }

    // Calculate mean:
    var average = sum / answers.length;

    if ( isNaN(average) ){
        // If mean couldn't be calculated, just enter 'N/A':
        var output = "N/A"; 
    } else {
        // Round to 2 decimal places & add the '/10':
        var output = average.toFixed(2).concat("/10");
    }   

    // Write to open text questions:
    f('av'.concat(i +1)).set(output);
}

However, I'm still interested to know of a quicker way.