Please note that this is an array formula. You create array formulas in the
same way that you create other formulas, except you press CTRL+SHIFT+ENTER to
enter the formula. If successful in 'Formula Bar' you can notice the curly
braces at both ends like "{=<formula>}"
=MIN(IF((MOD(COLUMN(G5:AA5),4)=3)*(ISNUMBER(G5:AA5)),G5:AA5))
=MAX(IF((MOD(COLUMN(G5:AA5),4)=3)*(ISNUMBER(G5:AA5)),G5:AA5))
=AVERAGE(IF((MOD(COLUMN(G5:AA5),4)=3)*(ISNUMBER(G5:AA5)),G5:AA5))
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