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Speed Math by Gaurav Tekriwal

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CHAPTER5

Checking Your Answers with Digit Sums

In This Chapter

  • Digit sums explained
  • Casting out nines to further simplify your calculations
  • Creating a nine-point circle and understanding how it works
  • Checking your addition, subtraction, multiplication, and division answers using digit sums

In previous chapters, you learned speedier ways to solve addition, subtraction, multiplication, and division problems. But how do you know if they’re right?

In this chapter, I talk about the concept of digit sums, which can help you check your calculations in a simple—not to mention quick—manner.

What Are Digit Sums?

The word digit means numbers like 1, 2, ...

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