How many phones were sold at the wrong price?

Mathematics
Tutor: None Selected Time limit: 1 Day

An error occurred in your bookkeeping department this month. The price of one of the smart phones that you sell is $489. Several customers were charged $565 for the phone instead. You know that the total sales for this month were $213,873 and that 401 phones were sold.

Sep 12th, 2015

Thank you for the opportunity to help you with your question! Hope your day is going well!

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

489x+565y=213873

But we also know that a total of 401 phones were sold, so we take the sum of x and y

x+y=401

The work:

Multiply the second equation by 489, and then subtract the two equations to solve for y

489x+565y=213873

489(x+y=401)

489x+565y=213873

489x+489y= 196089

76y=17784  (divide by 76)

y=234

Substitute y=234 into x+y=401

x+234=401

x=167

Let's do a check of our work. Substitute x and y into 489x+565y=213873

489(167)+565(234)=213873  CHECK!

Therefore the answer is

234 phones were sold at the wrong price.




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Sep 12th, 2015

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