Dynamic reference to sheet name

How can I insert a variable or cell value into a function to make the
reference (or worksheet) dynamic?

Imagine that there are four worksheets named: Summary, apples, oranges and
bananas. On the Summary sheet the first column contains one of the other
worksheet names, eg all values in column A contain one of the worksheet
names: apples, oranges or bananas. Cells in other columns contain references
that leverage the worksheet names in column A. For instance, something like
the following:
=average(<A1>!B1:B30)
=average(<A2>!B1:B30)

My question is, what should I replace <A1> with such that it substitutes in
the value from the first column which will match one of the worksheets in the
workbook?

Darien0104 wrote:
> How can I insert a variable or cell value into a function to make the
> reference (or worksheet) dynamic?
>
> Imagine that there are four worksheets named: Summary, apples, oranges and
> bananas. On the Summary sheet the first column contains one of the other
> worksheet names, eg all values in column A contain one of the worksheet
> names: apples, oranges or bananas. Cells in other columns contain references
> that leverage the worksheet names in column A. For instance, something like
> the following:
> =average(<A1>!B1:B30)
> =average(<A2>!B1:B30)
>
> My question is, what should I replace <A1> with such that it substitutes in
> the value from the first column which will match one of the worksheets in the
> workbook?

=AVERAGE(INDIRECT("'"&A1&"'!B1:B30"))