trigger UpdateQLIs on Quote (before update) {

    list<id> qids=new list<id>();
    for(Quote q:trigger.new)
    {
        Quote OldObj=trigger.OldMap.get(q.id);
        if(q.Total_Number_of_System_Groups__c != oldobj.Total_Number_of_System_Groups__c)
            qids.add(q.id);
    }
    System.debug('quote ids '+qids);
    list<QuoteLineItem> qlis=[select id, quoteID from QuoteLineItem where quoteID in: qids];
    System.debug('qlis '+qlis);
    for(quote q:trigger.new)
    {
        for(quoteLineItem qli:qlis)
        {
            if(qli.quoteID==q.id)
            {
                qli.Markup_Percent__c=q.Total_Number_of_System_Groups__c;
                update qli;
            }
        }
    }

}