00:03
It is given sequence of numbers are there, 15, 17.
00:07
The groupings have given as 1, 5, 9, 13.
00:12
First group is 1, 2nd group is 5, 9, 13, then 3rd group is 15, 19, 23, 27, and so on.
00:26
The groupings we have, i'm sorry, it's 5, 9, 13, 17, 21.
00:34
It's a gap of 4.
00:36
I will again write a groupings, third grouping here.
00:40
We have 4, 17, 21, 25, 29 and then 33.
00:48
That is the third grouping we have.
00:49
So we need to find out the first element in the first element in the 15th group.
01:00
So that what we can do, first we find out the number of elements in the 15th group.
01:05
So we have number of elements in the 15th group, number of elements.
01:13
In 15th group.
01:16
In the first group, number of element is 1, second group 2, 3, 3rd group 5, and so on.
01:21
So generalize it, it is 2n negative 1 for n equals 15.
01:26
That's coming out to be 29.
01:30
Number of sequence in the first 14 groups.
01:33
So sum of elements we have in the first 14 group, what we do, first we find out some of element in the first 14 root.
01:40
Then we find out the last element in the 14th group.
01:44
Right.
01:45
See, the idea is here.
01:47
For example, the second group is here...