Answer:
b. X1 + X2 ≤ X3 + X4
Explanation:
b. X1 + X2 ≤ X3 + X4
The situation tells us that the sum of both 1 and 2 must be equal to the sum of 3 and 4 which is true, because if both projects 1& 2 are selected then the both projects 3 & 4 must also be selected.
The rest of the choices are wrong because
a. X1 + X2 ≤ 2(X3 + X4)
The sum of projects 1& 2 is not less than 2 times sum of projects 3 & 4 .
c. X1 − X3 = X2 − X4
If we leave project 3 then project 4 cannot be left out.
d. X1 + X2 + X3 + X4 ≤ 2
any two projects out of the four cannot be chosen. 1 must be chosen from 1&2 and the other from 3 &4.