To simplify the expression, we can follow the order of operations (PEMDAS/BODMAS):

C = 25(-1/3)^3 + 1/5 - 2(-1/2)^2 - 1/2

First, let's simplify the exponents:

C = 25(-1/27) + 1/5 - 2(-1/4) - 1/2

Next, let's multiply and divide:

C = -25/27 + 1/5 - (-2/4) - 1/2

C = -25/27 + 1/5 + 1/2 - 1/2

Now, let's find a common denominator for the fractions:

C = -25/27 + 2/10 + 5/10 - 5/10

C = -25/27 + 7/10 - 5/10

C = -25/27 + 2/10

Next, let's convert the fractions to have a common denominator:

C = -250/270 + 54/270

C = (-250 + 54)/270

C = -196/270

Finally, let's simplify the fraction:

C = -98/135

Therefore, the simplified value of C is -98/135.