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Well, let's write down what we know
We know the price of the smart phone should 489
But several customers were charged 565
Let's say x= is the number of phones that was sold at the right price
y=is the number of phone sold at the wrong price
But we also know that a total of 401 phones were sold, so we take the sum of x and y
Multiply the second equation by 489, and then subtract the two equations to solve for y
76y=17784 (divide by 76)
Substitute y=234 into x+y=401
Let's do a check of our work. Substitute x and y into 489x+565y=213873
Therefore the answer is
234 phones were sold at the wrong price.
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