random given me 2 string not one

in quiz game this code give me 2 string not one from the list? i don't know why? i want one string from the list (alpha):

else if(qanswer.toLowerCase() == 'joker') {
        var alpha = [nia++,nca++];
        var beta = Math.floor(Math.random() * alpha.length);
        /*var gama = alpha[beta]*/
        var gama = alpha.splice(beta, 2);
        gama;       // lucky answer
        var seeansw = '<strike>'+ qanswer +'</strike><h4 id="iansw">Joker:</h4><div id="canswer">'+ canswer +'</div>';
      }

question 2 : this code give me the precent it's work but give me numbers with 9 digits like 66.66666666666 , i want only one digit after comma.

perc = (nca / nqansw) *100;