Estimation

EAD = O+4M+P/6

SD = P-0/6

Variance = SD^2

 To calculate the range of estimate what is correct formula from below-

1) EAD+/- SD i.e EAD-SD to EAD+SD

or

2) EAD +/- Variance i.e. EAD - Variance to EAD+Variance