Getting Avg from nth number of rows

[nina2018]

Hello Everyone,
I have tried so many options but just can't find the answer yet.
Scenario is as follows...
values are from A3 to A1082
i want to get the value from A3, A18 (A3 + 15), A33 (A18+15), A48 (A33 + 15), A63 (A48 + 15).... so on.. till A1082 and calculate the average of it.
I know the answer can be obvious but i just cannot seem to get the right answer.
Any help will be highly appreciated.

Thanks in advance!

[Fluff13]

How about
=AVERAGE(IF(MOD(ROW($A$3:$A$1082)-3,15)=0,$A$3:$A$1082,0))

...confirmed by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER. You will know the array is active when you see curly braces { } appear around your formula. If you do not CTRL+SHIFT+ENTER you will get an error or a clearly incorrect answer.

[kvsrinivasamurthy]

Slight correction in the above ARRAY formula

=AVERAGE(IF(MOD(ROW($A$3:$A$108)-3,15)=0,$A$3:$A$108,""))

[nina2018]

Thank you so much for replying. But the answers are not exactly right.
The Answer for the first row A3 is right but the rest is not.
The last row is A1082 and that is fixed but the first row changes from A3, A4, A5.... to A1082 sequentially.
so the calculation should be average of (A3, A18(A3+15), A33(A18+15)....... in cell J3 as an answer
A4, A19(A4+15), A34(a19+15).... in cell J4 as an answer
i hope you are understanding me.

[AliGW]

Will you please attach a sample Excel workbook? We are not able to work with or manipulate a picture of one and nobody wants to have to recreate your data from scratch.

1. Make sure that your sample data are REPRESENTATIVE of your real data. The use of unrepresentative data is very frustrating and can lead to long delays in reaching a solution.

2. Make sure that your desired results are also shown (mock up the results manually).

3. Make sure that all confidential data is removed or replaced with dummy data first (e.g. names, addresses, E-mails, etc.).

4. Try to avoid using merged cells as they cause lots of problems.

Unfortunately the attachment icon doesn't work at the moment, so to attach an Excel file you have to do the following: just before posting, scroll down to Go Advanced and then scroll down to Manage Attachments. Now follow the instructions at the top of that screen.

Please pay particular attention to point 2 (above): without an idea of your intended outcomes, it is often very difficult to offer appropriate advice.

[kvsrinivasamurthy]

ARRAY formula in C3 then drag down.

=AVERAGE(IF(MOD(ROW($A3:$A$1082)-ROW($A3),15)=0,$A3:$A$1082,""))