1) Provided by etramway, Time Value of Money Theory with downloadable study guide takes 8:13.

3) Provided by the Khan Academy, takes about 40 minutes.
     Introduction to Present Value 10:19 A choice between money now and money later.
     Present Value 2 10:11  More choices as to when you get your money.
     Present Value 3 7:42 What happens when we change the discount rate?
     Present Value 4 (and discounted cash flow) 10:02  Change discount rates depending on how far out are the payments.