how to find the element in Binary index tree

I have an array of elements A[] which are not zero now what i want to do is to update
range of elements.Then i want find the element at a particular index.
Suppose if a have an array like this A[]={4,6,7,3,2};

After inserting this elments in BIT the BIT look like BIT[]={4,10,7,20,2}

After doing
Update:2 3 5

Update:3 5 2

The elements in binary index tree are {4,15,9,22,2}

Now i want to find the element at particular index How can i find it ?
Please correct if there is anything wrong in the question.

you can find the sum of first i elements in O(log N), let it be sum(i)

then the element at any index,say j is sum(j)-sum(j-1)