update the subsequent rows at each change in other column

[pavan.dhoke]

Hi,
I want to update the subsequent rows at each change in other column
the sample file is attached in which there are 2 columns
A and B
I want to update the NEW column at each change in OLD column
I have manually shown as how it should be updated

A formula or a Macro will resolve my problem

OLD NEW
AAA AAA01
AAA AAA02
AAA AAA03
AAA AAA04
AEE AEE01
AEE AEE02
AEE AEE03
AEE AEE04
ADR ADR01
ADR ADR02
ADR ADR03
Thanks in advance

[teylyn]

Hello,

maybe in B2 and copied down:

=A2&TEXT(COUNTIF($A$1:A2,A2),"00")