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300 exercise books are arranged into 3 piles. The first pile has 10 more books than the second pile.
The number of books in the second pile is twice the number of books in the third pile. How many books are there in the third pile?

first look at what you know:

1) the TOTAL number of books IS 300

2) there are 3 piles
this tells you you will add
3 things

What do you NOT know?
the number of books in the
third pile
use the letter "x" for this

now try to put your problem together

pile 1 pile 2 pile 3

+ + x = 300

see if you can figure it out now.

If I were you, I'd put it like this:

300 divided into 3. That would be 100.

It says 1st pile has more books than 2nd pile. 10 books, right? Ok.

100 - 10 = 90, right?

So, 1st pile has 110 books.

The 2nd pile NOW has 90 books.

The third pile is untouched. It has 100 books.

Now multiply 100 times 2. You'll get 200.

The 2nd pile has 290 books.

While the 3rd pile has 100.

o_O <<< Uh, get what I mean?

And if I'm missing something big here, please correct me. (Sorry, I can't tell my email address, it isn't allowed.) Thanks.

I think the 1st and 2nd pile are just "confusers". Well, can't really tell what's the answer. I ain't no expert. =)

Tip: Maybe you have to solve it on your own. Or, follow the 1st response.