Weighs it all up and buys an interest in (5,5)

I believe the answer is:

takes stock

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'weighs it all up' is the definition.
I can't judge whether this defines the answer.

'buys an interest in' is the wordplay.
'buys' becomes 'takes' ('take' can be a synonym of 'buy').
'an interest in' becomes 'stock' (I can't justify this - if you can you should believe this answer much more).
'takes'+'stock'='TAKES STOCK'

'and' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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