That depends ... on what X and Y are!
And if that does not come naturally to you, perhaps you should read The Complete Idiot's Guide to Pre-Algebra by Amy Szczepanski and Andrew Kositsky.
The CIG to PA is built just like the other books in the Idiot's series, using familiar conventions to keep the flow of the book smooth while providing additional ancillary information, and in the case of this text, practice problems (answers provided in the back). This book reminds me of a tired old reference I've got on my shelf called Technical Mathematics. Sometimes you just need a place to look up the formula for the volume of a cone.
~ A repost for Back to School Special ~
I've compared the contents and methods of presentation of this book to the equivalent textbook Julia used in school last year (7th grade math = pre Algebra in Minnesota) and found the Idiot's guide to be simpler, more straightforward, less confusing as a book, and better presented. However, the textbook (which is pretty standard textbook) is much better designed to use in a math class. Our school district uses a technique called "spiral learning" in which the same topic is revisited again and again and again ... first introduced, then in depth, then reviewed, then reviewed again later on. This makes for a text that is hard to use if you want to go fast or just look something up, but it is great in a classroom setting where a teacher is working with a well designed syllabus and other materials.
But out of the traditional classroom, as summer reading so your kid can be smarter than the other kids, as a review before delving into HS or even College algebra, or as a home schooling book, the CIG for Pre-Algebra works very nicely and is highly recommended.
What is Pre-Algebra (so you know, whether this book fits your needs or not)? The definition of Pre-Algebra probably varies a bit from place to palce and time to time, but here's a rough list of topics:
Basic number theory ... remember all those different kinds of numbers, like "natural" and "whole" and "skimmed" (no, wait, "skimmed" is milk, not numbers).
Addition, subtraction, multiplication and division ... (so what, you say!!!) of not just numbers but of exponents, decimals, negative and positive terms, and exponents. Ultimately, these are many of the basic rules you will need in algebra.
Basic expressions ... what re they ... and introduction to equations.
Geometry (areas, volume, etc. etc.) including the beginning of triangles. (Triangles are not just shapes, but rather, the beginnings of some heavy concepts. I mean after all, a whole branch of math is named after them ... Trigonometry. There is a reason we've never heard of Squarometry!)
Basic data analysis: Collecting data, display and basic analysis, and probability.
I cannot promise you that this book matches exactly your local state standards for pre-algebra math, but my sense is that it would for almost all possible users.
These sorts of books tend to make rather useless textbooks, but supplement classroom texts quite nicely. I also suspect that they are most useful when parents sit down with their kids to help them use them. The problem is that kids who need supplementary texts the most, are the least likely to use them efficiently or even use them at all. I know that when I was in primary school, I wouldn't have had the least desire to even touch this book, while a history supplement (I was tutoring a couple of seniors when I was a freshman) would have been awesome.
If you have a child young adult who is having trouble with a given subject, it makes a big difference if you actually work with them.* Texts like this one are absolutely wonderful in this context, especially if the subject is not one of your strong suites either. This can also be a great way to connect, as you work on learning what they need to know alongside them.
This is not to say that I don't believe very strongly in self-directed learning - I absolutely do. But when your child is struggling, you can be an invaluable resource. Though if you have problems with patience, tolerance and/or empathy, this probably doesn't apply to you. That is not a values judgment either, just pragmatic.
*Of course this presupposes you have worked with them all the way through. As preteens and teens, they are not all that likely to accept your help otherwise - for that matter, it will be hard enough if you have been working with them.