Here are a couple of articles that may be of use to you, as well as a site for you to convert any compounding method into an annual effective interest rate:

http://www.quickanddirtytips.com/educati...

http://www.quickanddirtytips.com/educati...

http://www.moneychimp.com/articles/finwo...

For #52A use: http://www.wolframalpha.com/input/?i=x+%...

50) how long will it take money to double if it is invested at

A) 8% compounded semiannually?

B) 7% compounded semiannually?

52) How long will it take money to double if is invested at

A) 21% compounded continuously?

B) 33% compounded continuously?