android - how to prevent reselected checkbox from adding more value -

i have created survey layout question , can select below avg, avg or above avg. score @ bottom of page , updates on click via listener.

i have problem customer changing answer , not removing pervious value.

so below 1 , avg 2 , above 3. if click above adds 3 , change mind , want pick avg , click , adds 2 never removes pervious 3.

help

    below32 = (checkbox) findviewbyid(r.id.below32);     below32.setonclicklistener(new view.onclicklistener() {         public void onclick(view v) {             if (below32.ischecked()) {                 sum += 1;      double total = 100*sum/69;                 result.settext(string.format("%.1f", total) + "%");                 avg32.setchecked(false);                 above32.setchecked(false);             }             else {                 sum -= 1;      double total = 100*sum/69;                 result.settext(string.format("%.1f", total) + "%");             }         }     });     avg32 = (checkbox) findviewbyid(r.id.avg32);     avg32.setonclicklistener(new view.onclicklistener() {         public void onclick(view v) {             if (avg32.ischecked()) {                 sum += 2;      double total = 100*sum/69;                 result.settext(string.format("%.1f", total) + "%");                 below32.setchecked(false);                 above32.setchecked(false);             }             else {                 sum -= 2;      double total = 100*sum/69;                 result.settext(string.format("%.1f", total) + "%");             }         }     });     above32 = (checkbox) findviewbyid(r.id.above32);     above32.setonclicklistener(new view.onclicklistener() {         public void onclick(view v) {             if (above32.ischecked()) {                 sum += 3;      double total = 100*sum/69;                 result.settext(string.format("%.1f", total) + "%");                 below32.setchecked(false);                 avg32.setchecked(false);             }             else {                 sum -= 3;      double total = 100*sum/69;                 result.settext(string.format("%.1f", total) + "%");             }         }     }); 

what need change or make work? other attempts have failed.