Well, it is quite possible that the jQuery plugins which are used are dependent on older version but for your own jQuery code, you would like to use newer version. So because of this dependency, multiple version of jQuery may required sometimes on single page.
Below code shows how to include multiple version of jQuery.
var $jq = jQuery.noConflict();
By this way, for your own jQuery code use "$jq", instead of "$" as "$jq" refers to jQuery 1.9.1, where "$" refers to 1.7.2.