i am stuck on the following PERT PROBLEM
WHICH IS 60% SOLVED. SO FAR I HAVE:

DURATION IN WEEKS

(i) ACTIVITY A
10 LIKELY
5 OPTIMISTIC
21 PESSIMISTIC

(ii) ACTIVITY B
6 LIKELY
4 OPTIMISTIC
8 PESSIMISTIC

(iii) ACTIVITY C
14 LIKELY
6 OPTIMISTIC
16 PESSIMISTIC

(A) CALC THE EXPECTED DURATION PER ACTIVITY
(i) 5+5*10+21/6 = 11
(ii) 4+4*6+8/6 = 6
(iii) 6+4*14+16/6 = 13

total 30 weeks EXPECTED PROJ DURATION

(B) DETERMINE THE STD DEVIATION

A 21-5=16/6=2.67
B 8-4 = 4/6=0.67
C 16-6 = 10/6=1.67

((2.67)^2 + (O.67)^2 + (1.67)^2)^0.5

= 3.21

(C) ASSUMING A NORMAL DISTRIBUTION ESTIMATE THE PROB THAT THE
PROJ DURATION IS

(i) more than A days (ii) less than B days (iii) between C and D days

I am stuck on Part C. Note I have weeks and days. Do I convert days into weeks to make the whole thing equal? My problem is knowing (i) what figure used to subtract A, B and C&D days. Once I have clarity here
I can go ahead and work out the confidence limits. Thanks