Question

a=b+c-2
a=c-d+9
a=b-d+11
Based on the system of equations above, what is the value of a?
a) 2
b) 9
c) 10
d) 11
e) 20

Answer 1

can't tell. There are 4 unknowns, but only three equations. Any system where

c = b+2
b+d = 11

will work. For example, the table below shows various values of a

b c d a
1 3 10 2
2 4 9 4
. . .