prepositions

[economicus]

Hi,
I need some help from native english speakers at prepositions:

They exploit artificial limitations of people by satisfying their social needs.

Is this preposition correct? Would it be better with at or in?

What about: They are useful at helping you to come through. [by, in??].

What's the difference between by and at?
Thank you.

[wasleys]

Hi,
I need some help from native english speakers at prepositions:

They exploit artificial limitations of people by satisfying their social needs.

Is this preposition correct? Would it be better with at or in?

What about: They are useful at helping you to come through. [by, in??].

What's the difference between by and at?
Thank you.

Economicus,

Perhaps these examples will help.

I find no pleasure in washing cars.
Are you good at washing cars?
Then you can help me by washing my car.

In those both in and at roughly = in/at the act of, and by = through the act of/by means of.

So in your examples I think the first needs by (but I am not sure what you mean in the sentence) and the second needs at.

There are other uses, especially of by.

Post back if that's not clear.

Michael