Actually I am using Sumif function

In A2:A5 in sheet 1 is Date

Like
<30
<60
30
60

In Sheet2 in A2:A300
30
<60
<30
<60 and so on

Sheet2 B2:B300

100
200
300
500
600
800 and so on

Now When I use =sumif(Sheet2!A:A,Sheet1!A2,Sheet2!B:B)

And it shows 0 in all Cells

But one of My friend Suggest me to Put dot or Comma Before Data in A:A in
Sheet 1 and Sheet2

Like .<30 or ,<60 and so on

It works perfectly.

But unfortunately my Friend dont know the why it happened

Could you please suggest me why it happened?

Thanks in Advance

Hardeep kanwar