'problems understanding his theories' vs 'problems in understanding his theories'

[Hanifasmm]

Usage of the preposition IN:

Hi,
1. Einstein was so intelligent that some other scientists
had problems understanding his theories.

2. Einstein was so intelligent that some other scientists
had problems -in- understanding his theories.

Could you please confirm that "in" in the second sentence is
grammatically correct?

Thanks,
Er.S.M.M.Hanifa

[Alan]

Hi,

'In' is acceptable in your sentence and simply extends the use of 'problems'.

Alan
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English as a Second Language
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