Do Double Digit Multiplication

Don't be intimidated by double digit multiplication. As long as you know how to do basic single-digit multiplication, you're already on your way. Really, all you have to do is multiply the digits in the first number by the ones digit of the second number, then multiply the digits in the first number by the tenths digit of the second number, and then add up the two products. If you want to know how to quickly and easily master this process, just see Step 1 to get started.

Steps

1. Write down the problem. Just write one number above the other, with a little multiplication (x) sign to the left of the bottom number. Let's say you're working with the following problem: 22 x 43. Write "22" above 43 with a line below the 43. You can also place the other number on top -- it makes no difference when you're multiplying two two-digit numbers.
2. Multiply the number in the ones place of the bottom number by both digits of the top number. The "3" is the number in the ones place in the number 43. First, multiply 3 by the number in the ones place of the top number 22, 2, to get 6. (3 x 2 = 6.) Write a "6" below the 3. Then, do the same with the number in the tens place of 22, which also happens to be 2. You'll get six again. This time, write the "6" below the 4 to get "66" in the row below the multiplication bar.
   • Let's say you were multiplying 52 x 43 instead. Then, you would still multiply 3 by 2 to get 6, but then you would multiply the 3 by 5 to get 15. You'd get 156 in the row below the multiplication bar.
   • It's not always this easy. If you multiply the number in the ones place of the bottom number by the number in the ones place of the top number and get a number greater than 9, then you'll have to carry the number in the ones place of the product over to the tens place of the number in the top row.
     • For example, if you were multiplying 26 x 43, you would multiply 3 by 6 to get 18. You'd write the 8 below the 3, but you'd carry the 1 (the number in the tens place of the product) above the 2 in 26. Then, you'd multiply 3 by 2 to get 6, but you'd also add that extra one to get 7 in the ones place of the product. 26 x 3 = 78, so you'd write 78 underneath the multiplication bar before you move on.
3. Write a "0" in the units column below the first product. Now, place a "0" below the first 6 in 66. This accounts for the fact that you'll be multiplying numbers in the tens column of both the numbers 22 and 43.
4. Multiply the number in the tens place of the bottom number by both digits of the top number. Do the same thing you did with the "3" of 43 with the "4" of 43. First, multiply the 4 by the second 2 of 22 to get 8 (4 x 2 = 8). Write the 8 down below the first 6 in 66, to the left of the zero. Then, multiply the 4 by the first 2 in 22 to get 8 again. Write the 8 to the left of the first 8 you wrote down. You'll get 66 in the top row and 880 in the row below it.
   • Remember that the same rules of carrying numbers apply here. If you multiplied the 4 by a number larger than 2 in the ones place, you'd get an answer larger than 9 and would have to carry the number in the tens place of the result over the number in the tens place of the top number.
5. Add up the two products. This means you'll have to add up the numbers in the two rows below the multiplication bars. You're left with 66 on top and 880 on the bottom. Just add them up to get the answer. 66 + 880 = 946, your answer. You can use your calculator or do this manually.
   • If you do it manually, you first add the 6 in the ones place of the first number and the 0 in the ones place of the second number to get 6 in the ones place of the final answer. Then, you add the 6 in the tens place of the top number and the 8 in the tens place of the bottom number to get 14, writing down 4 to the left of the 6 and carrying the 1 over the stand-alone 8. Then, you add 1 and 8 to get 9, which also gives you 946, your final answer.

Tips

• Use a calculator to check your work.
• Go slow. If you need to write it into 2 separate problems.

Related Articles

• Divide Double Digits
• Learn the 9's on the Multiplication Table
• Learn Multiplication Facts
• Teach the Multiplication Tables to Your Child
• Study for a Math Exam
• Do Subtraction Using a Fast Calculating Method

Sources and Citations

• http://www.khanacademy.org/math/arithmetic/multiplication-division/multi_digit_multiplication/v/multiplication-5---2-digit-times-a-2-digit-number
• http://www.mathplayground.com/multiplication05.html

See also

• Teach the Multiplication Tables to Your Child
• Do Long Multiplication
• Do Long Division
• Do Short Division
• Multiply
• Divide Square Roots
• Multiply Mixed Numbers
• Divide a Whole Number by a Decimal
• Find the Greatest Common Divisor of Two Integers
• Divide Double Digits

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