Question 1159711
<br>
The answer from the other tutor contains a simple arithmetic error which leads to a nonsensical answer -- the average cost per dozen can't be $1.65 if the prices per dozen are $1.50 and $1.25.<br>
You can solve the problem with formal algebra the way that tutor tried.<br>
Or you can use this informal method, which (if you understand it) will get you to the answer much faster and with much less work.<br>
The store bought 200 dozen pens at $1.50 per dozen and an additional 50 dozen at $1.25 per dozen.  So 200/250 = 4/5 of the pens were bought at the higher price.<br>
That means the average cost per dozen is 4/5 of the way from the lower price to the higher price.<br>
The difference between the two prices per dozen is 25 cents; 4/5 of that is 20 cents.  So the average cost per dozen is $1.25+$0.20 = $1.45.<br>