理解不了关于PV FV PMT正负号的取舍 什么时候用正号 什么时候为负号

An investor purchased an annuity many years ago. The first payment of the annuity is to be received today. Assume the payment of the annuity is $5,000 constanly , the period the payment is 20 years. and the discount rate is 12%, calculate the today' value of the annuity:

您的回答A, 正确答案是: C

A

不正确$37,347.

B

$403,493.

C

$41,829.

Under the BGN mode.

N = 20; PMT = -5,000; I/Y =12; FV = 0; CPT PV = 41,828.89.

PMT为什么要用-5000

The first payment of the annuity is to be received today. 这句话在题干中什么意思，最先一笔年金于今天收到？？？