find duplocates with multiple criteria

[martinblake02]

type	amount
flour	1g
four	2g
rice	5g
veg	2g
meat	1g

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</tbody>

hello,
I am still new to this forum and hope im asking in the right place.

I have a table with duplicate in column B, and values In column a.
I want to calculate how many duplicates I have in column b If column a = 1 or 2 (two options)

example is above.
so if told my formula that a could be flour or meat, the result would be 1 duplicate (1g)

therefore I need a formula like below, but I cant get anything to work:
if column a = "flour" or "meat" , count of duplicates = 1

 

[PCL]

In case there is several duplicate values, how do you want to display results ??