add 5(0.5k - 1) + 2 (0.4 - k). answer should be in decimal form

To solve the expression, we distribute the numbers and combine like terms:

5(0.5k - 1) + 2(0.4 - k)
= 2.5k - 5 + 0.8 - 2k
= 0.5k - 4.2

Therefore, the answer is 0.5k - 4.2.