# 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?

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

Just another alternative using similar concept as Ender.