Answer:
Decreased by 20%
Explanation:
0.5 x ? = 0.4
? = 0.4/0.5
? = 0.8
1 - 0.8 = 0.2
0.2 = 20%
To check, 20% of 0.5 is 0.1. 0.5 - 0.1 is 0.4. So the answer is correct.
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