AVERAGEIFS - Multiple Columns, Multiple Criteria

Would someone please be able to help with a formula to average multiple columns based on multiple criteria?

Attached is example data. I need to average tab 1 column B, if tab 1 column A=6/30/2019, combined with averaging tab 2 column B, if tab 2 column A=6/30/2019 in the same formula.

In the attached example data, the correct answer should be 29%.

I have tried the formula =AVERAGE(AVERAGEIF('Tab 1'!A:A,"6/30/2019",'Tab 1'!B:B),AVERAGEIF('Tab 2'!A:A,"6/30/2019",'Tab 2'!B:B)) but it comes up with the wrong result.

I think I need to use AVERAGEIFS but not sure how to include multiple columns in the average range.

Taking the average of averages will only give you an accurate result if the number of items in each average is the same (or if both averages are 0).

Try this:

=(SUMIF(A:A,DATE(2019,6,30),B:B)+SUMIF('Tab 2'!A:A,DATE(2019,6,30),'Tab 2'!B:B))/(COUNTIF(A:A,DATE(2019,6,30))+COUNTIF('Tab 2'!A:A,DATE(2019,6,30)))