Libros de April Barth :

When you do no need to know an exact amount, you can estimate. See how to estimate sums and differences.

Some objects look like solid shapes! Learn how to use special words to describe where the objects are.

See how models, the hundred chart, and number lines are used to compare numbers. Use special words to compare numbers.

Did you know that addition and subtraction are related? See how fact families can help you find sums and differences.