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Our school uses the Official Singapore Math workbooks in the classroom. I prefer these as the provide the strategies involved in each section. I also like that it really builds a solid foundation. The pictograph exercises provide a great foundation for moving into bar graphs. As a mathematician, I also appreciate that these books also delve into the "why" and just don't focus on the "how".
For parents, they are nice as many aren't familiar with Singapore Math methodology. For some of us, we've been doing this for years.
As for the number of problems. I think the more math exercises one can do the better. Just like physical exercise. 1 sit-up a day is better than none, but it's not going to make you any fitter.
Purchased this book to reinforce what my son had learned at the end of 2nd grade (his school uses Singapore Math). It's what I was expecting, and there is an answer key at the end of the book. It shows how they expected the problems to be solved as well.
I did like this book even though it is aligned with common core standards. It was challenging but not difficult for my 1st grader that I homeschool. I just don't like the extra steps that he has to take to find the answers.
This practice book is great and goes right along side Singapore Math at the same level. You can skip parts that your child doesn't need extra review on or just move along right with the book, completing each section with the curriculum. We are homeschoolers and love Singapore Math and it's practice books.