EAC Formula

 Hi,

I have been cough by this doubt while doing an exercise on EAC.

36.You are a project manager working for Mail House King. Your com-pany processes orders for several mail-order catalog companies. Your project is to install new mail-sorting equipment and software. YouÕve had some problems and experienced some variances so far during the project. You expect these variances to continue throughout the life of the project. Your project sponsor has asked for an EAC. You know the following information: PV = 800, BAC = 700, EV = 675, AC = 750, and ETC = 30. Which of the following is the correct EAC given the circumstances?

A.778

B.780

C.861

D.833

 

I expected the formula to be  EAC= AC + (BAC-EV)/(CPI*SPI) as per the formula on Rita book.

 

But the solution used this foruma: EAC=AC+(BAC-EV)/SPI only..

36.C. The question says that the variances youÕve experienced to date are expected to continue throughout the project. The formula for EAC given these circumstances is as follows: EAC = [AC + (BAC Ð EV) CPI] . CPI = .9. Therefore, our calculation looks like this: [750 + (700 Ð 675)  .9] = 861.11, or 861 rounded down.

 

Any help??