For better understanding, we can take an array/list arr =[1,2,3,4,5,6,7,8,9] Sub-Array/Sub-strings: It provides an array that contains one or more than one elements of any specific array. The small or sub-array element will be continuous of the main array. Example: [4,5,6,7], [1,2,3], [2], [5], [9,10] that is all about of subarray. But [1,3,8] is not sub-array cause the element are not continuous. How many sub-array will be possible that calculate this low (n*(n+1))/2