Q:

# How do you do double digit multiplication?

A:

To multiply two-digit numbers, write the first number on a piece of paper and write the second number directly underneath it. Multiplying double digits requires breaking the problem into four multiplication equations and one addition calculation.

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1. Multiply the second digits

Multiply the last digits of both numbers together. For example, in 12 x 15, calculate 2 x 5 = 10. Write this answer below the two starting numbers.

2. Multiply the last digit of the second number

Replace the second digit of the first number with zero. Multiply the entire top number by the second digit of the second number. So in 12 x 15, calculate 10 x 5 = 50. Write this answer below the number calculated in the first step.

3. Multiply the first digit of the second number

Replace the second digit of the second number with zero. Multiply this number by the second digit of the first number. In 12 x 15, multiply 10 x 2 = 20. Write this answer under the number calculated in the second step.

4. Multiply the first digits

Replace the second digits of the first and second numbers with zero. Multiply these together. In 12 x 15, multiply 10 x 10 = 100. Write this answer under the number calculated in the third step.

Add the four calculated numbers to find the answer to the original multiplication problem. For example, in 12 x 15, add together 10 + 50 + 20 + 100, which equals 180.

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