In your business, you always need to know what to pay for something - an asset, for example, like a monetary investment or plant and equipment. In order to know what to pay for it, you have to able to calculate its present value. You will accrue payments from many types of investments. If these payments are equal and consecutive, they are called annuities. As a business person, you need to be able to calculate the present value of two types of annuities - ordinary annuities, which pays you payments at the end of a time period and annuities due, which pays you at the beginning of the time period, in order to know what to pay for your investments now.
These articles help you learn to make these calculations in a variety of ways!