Why my DOM is not removing checked attribute [duplicate]

This question already has an answer here:

• Remove attribute “checked” of checkbox 9 answers

I have 5 checkbox and only the first checkbox is not disabled. I want to remove disabled attribute when i checked the first checkbox from remaning checkbox and when i checked the second checkbox then the 3,4,5 checkbox get checked and if i remove the checked from first checkbox then all other checkbox also remove there checked property and get disabled.

function showdis(a){
  if(a.checked==true){
    for(i=2;i<=5;i++){
      $('#pay'+i).removeAttr("disabled");
    }
  }else{
    for(i=2;i<=5;i++){
      $('#pay'+i).removeAttr("checked");
      $('#pay'+i).attr("disabled",'disabled');
    }
  }
}
function selectAll(a){
  if(a.checked==true){
    for(i=3;i<=5;i++){
      $('#pay'+i).attr("checked","checked");
    }
  }else{
    for(i=3;i<=5;i++){
      $('#pay'+i).removeAttr("checked","checked");
    }
  }
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<input type='checkbox' id='pay1' onclick="showdis(this)">Remove Disabled
<input type='checkbox' id='pay2' disabled onclick="selectAll(this)">Checked 3,4,5
<input type='checkbox' id='pay3' disabled>3
<input type='checkbox' id='pay4' disabled>4
<input type='checkbox' id='pay5' disabled>5

Everything is working fine but when i unchecked the first checkbox its removing checked attribute from every checkbox except the second checkbox