Answer:
$12
Explanation:
"Of" means "times" in this context:
30% × $40 = 30/100 × $40 = $12
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% is a fancy way to write /100, so 30% = 30/100 = 0.30 (thirty hundredths).
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Since you're familiar with decimal multiplication, you know that you can rewrite this problem as ...
30/100 × $40
= 3/10 × $40
= 3 × ($40/10)
= 3 × $4
= $12