To solve this expression, we will first calculate the values of sin 30°, ctg 45°, and cos 180°.

sin 30° = 0.5ctg 45° = 1 (since cotangent is the reciprocal of tangent, and tan 45° = 1)cos 180° = -1 (cosine of 180° is -1)

Now, substitute these values back into the expression:

5(0.5) - 1 + (-1) = 2.5 - 1 - 1 = 0.5

Therefore, the final result of the expression 5 sin 30° - ctg 45° + cos 180° is 0.5.