Answer:
20 miles
Explanation:
It is useful to remember that % means /100, and that 1% = 1/100.
Here, you want 1/2% × 4000. The associative property of multiplication lets you rearrange this to ...
(1/2)% × 4000 = (1/2) × 1% × 4000
= 1/2 × (1/100 × 4000) = 1/2 × 4000/100
= 1/2 × 40 = 20 . . . miles
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If you refuse to be intimidated by percentages, you can do this math in your head.