Answer: Choice A) $16
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Work Shown:
5 notebooks = 20 dollars
5/5 notebooks = 20/5 dollars ..... divide both sides by 5
1 notebook = 4 dollars ..... unit rate
4*(1 notebook) = 4*(4 dollars) .... multiply both sides by 4
4 notebooks = 16 dollars
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Another approach:
(5 notebooks)/(20 dollars) = (4 notebooks)/(x dollars)
5/20 = 4/x
5*x = 20*4 ... cross multiply
5x = 80
5x/5 = 80/5 .... dividing both sides by 5
x = 16
So 4 notebooks cost $16
