How to use this set: Work straight through, unit by unit — each unit starts easy and builds toward its hardest problem. Try every question before checking the hint. As soon as you choose an answer, you'll see whether you're correct and get a full explanation, so you can learn as you go. Set your timer above to practice finishing within one hour, or turn it off and work at your own pace. When you're done, tap Print / Save PDF for a clean, ink-friendly copy with the answer key on the last page.