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Question

Ken bought some books at an average of $3.50 each. he bought another 2 books at $6 each and the average price became $4. how many books did he buy altogether?

Answer

post-18707

2 books at $6 average dropped to $4 average after combining with other other books. That is $2 dropped each making a total of $4.

Now this $4 dropped from the 2 books has affected the raise in average of the $3.50 books to $4. That is $0.50 each. In other words using this $4 dropped to raise the $3.50 books. They each rises by $0.50 and they also sum up to $4 to match the drop.

So below is the working,

Total dropped by the 2 books = total rises of the “$3.50” books = (6-4) x 2 = $4

Rise in each $3.50 average books = $4 – $3.50 = $0.50

The number of the average $3.50 books are = $4/0.50 = 8 books

Together with the other $6 average book , there are 8+2= 10 books.###

 

Here’s another example 

https://www.kiasuparents.com/kiasu/question/16998-2/

 

Edit note: Added a picture representation to describe my working. Acestarling style.

0 Replies 1 Like ✔Accepted Answer
post-18712-1

Just another alternative using similar concept as Ender.

1 Reply 2 Likes

Pictures speaks a thousand words. Got time, maybe I will draw one up too.

0 Replies 0 Likes