Question 135659
Your work is correct. 
When you changes from 17/3 to 5.67 you rounded the number up (made it larger)
That is why when you add 5.67+6.67+7.67 you have a sum of slightly more than 20.
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You could write your answer as (17/3), (17/3)+1, (17/3)+2
to get 3(17/3)+3 = 17+3 = 20
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Cheers,
Stan H.