If you want to find odd number of table rows then it's not a difficult task now, we can do this easily with the help of jQuery :odd selector.

The :odd selector will choose all those components which have odd index i.e 1,2,5 etc.

Most of the time we have to use :odd selector  together with another selector for choosing those  component which have odd index .

In below example we are finding all table rows which have odd index value with the help of :odd selector and then making their background  green.

Below is the html code for finding odd number of table rows  :-

    <table border="1">
    <tr><td> Index value 0</td></tr>
    <tr><td> Index value 1</td></tr>
    <tr><td> Index value 2</td></tr>
    <tr><td> Index value 3</td></tr>
    <tr><td> Index value 4</td></tr>
    <tr><td> Index value 5</td></tr>
    <tr><td> Index value 6</td></tr>
    </table>
    <button id="btn">Click to see the effect</button> 

Below is the jQuery code :-

    $('#btn').click(function(){ 
    $( "tr:odd" ).css( "background-color", "green" );
    });

working demo:-https://jsfiddle.net/e4xkfw83/1/