public class TasksViewer {
	
	public List<String> getTaskStats() {
        
        List<String> taskStats = new List<String>();
		Map<String, map<String, Integer>> ratingVsRecordCountMapOfmap = new Map<String, map<String, Integer>>();

		List<Task> lstAggResult = [Select Priority, Status From Task Where Priority != Null AND Status != Null];

		if(!lstAggResult.isEmpty()) {
		 for(Task objTest : lstAggResult) {
			   if(ratingVsRecordCountMapOfmap.containsKey(objTest.Priority)) {
					Map<String, Integer> innermap = ratingVsRecordCountMapOfmap.get(objTest.Priority);
					//if(!innermap.isEmpty()) {
						if(innermap.containsKey(objTest.Status)) {
						   Integer count = innermap.get(objTest.Status) + 1;
						  innermap.put(objTest.Status, count);
					   }
					   else {
						   innermap.put(objTest.Status, 1);
					   }
					   ratingVsRecordCountMapOfmap.put(objTest.Priority, innermap);
				   //}
				}
			   else {
					Map<String, Integer> innermap = new Map<String, Integer>();
					innermap.put(objTest.Status, 1);
					ratingVsRecordCountMapOfmap.put(objTest.Priority, innermap);
			   }
			}
		}
        for (String priority : ratingVsRecordCountMapOfmap.keyset()) {
            taskStats.add(priority + ': ' +ratingVsRecordCountMapOfmap.get(priority));
        }
        return taskStats;
	}
    
}

<apex:page controller="TasksViewer">
    <apex:pageBlock title="Tasks Stats">
        <apex:pageBlockTable value="{!TaskStats}" var="taskStat">
            <apex:column title="stats" value="{!taskStat}" />
        </apex:pageBlockTable>
    </apex:pageBlock>
</apex:page>