9 dollars is 4 dollars.
Let's find the percent form of the discount
=> 4 dollars / 9 dollars = 0.44
Now, let's convert it to percentage
=> 0.44 * 100% = 44%
Thus the discount is 44%
1.68 mm per year for 1.5 years could be rewritten as
(2.00-0.32) mm per year for 1.5 yrs.
Multiply: (1.5 yrs)(2.00-0.32)(mm/yr) = 3 mm + 0.48 mm = 3.48 mm
This approach makes use of the distributive property of multiplication.
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