My friend only sent invitation letter from university. His father had about 10 lakh on arub bank or some foreign bank forgot the name and they got visa. I had another friend he send bank statement with 10K but they didn't get visa.

Another case, one guy who is green card holder, having baby on last Dec and they had bank balance of 50k but their parents didn't get visa at first attempt. They sent all doc like letter from doctor and everything but visa was rejected. They tried again and got in second attempt.

You never know. For my case, My mom didn't get visa when I invited her for my graduation but when I invote her for my sons first birthday they gave visa. Only thing I send was $3900 bank balance + my two paystuffs and my letter nothing else.

Really you never know, I don't know what exactly they look for.