Answer
$0.4\%$
Work Step by Step
First: $$\text{average value}=\frac{153.2\text{ mg}+151.1\text{ mg}+152.0\text{ mg}+146.9\text{ mg}+149.8\text{ mg}}{5}=150.6\text{ mg}$$
From this we can get:
$$\text{percentage error}=\frac{150.6\text{mg}-150\text{ mg}}{150\text{ mg}}\cdot 100=0.4\%$$
