Q&A for How to Do Long Multiplication

Set aside first the zeros (but remember how many there are). Multiply the non-zero numbers, then add all the zeros that you set aside beforehand.

Use a calculator to check your answer, or if not possible, use long division to divide your answer by one of the numbers and see if you get the other number.

Money problems aren't too complicated, just do the problem like a normal one and put the decimal in front of the last two numbers.

You will know to carry the number over if it is a two digit number. The first of the two digits is the one that you carry over.

Punnet squares may be useful to a geneticist, but they're not applicable in most multiplication questions.

Yes, although it takes longer. Once you become comfortable with the multiplication process, it will be a much more efficient use of your time.

At first multiply the two numbers together as if there were no decimals points in either number. Then add up the number of decimal places to the right of the decimal points in both multipliers, and place the decimal point in the final product so that the number of decimal places in the product is the same as the total decimal places in the two multipliers. For example, 9.8649 multiplied by 7.3 equals 72.01377, with four decimal places in one multiplier, one decimal place in the other, and five decimal places in the product.

You would use short division in this case (because dividing by 3 is so easy). 3 goes into 5 once with a remainder of 2. 3 goes into 26 eight times with a remainder of 2. 3 goes into 21 seven times. The quotient is 187.

The second method is really the first method dressed a little differently. It's offered in the hope that some students might find in it an explanation of the first method.

The process is the same as with shorter numbers. You just have more partial products to add together at the end.

Multiply 323 by 25. That's 8075. Then place the decimal point three places to the left of the last digit (because there is a total of three digits to the right of the decimal points in the multipliers). The final answer is 8.075. (That makes sense, because 3 multiplied by 2½ is roughly 8.)

See Multiply Decimals .

Use the process shown above. You'll wind up with a product in the hundreds of thousands.

Go with your calculator.

Multiply one numerator by the other to get the new numerator. Multiply one denominator by the other to get the new denominator. Reduce the fraction if possible.

No method is better than a calculator.

Multiply 993 by 984. In the answer there will be five digits to the right of the decimal point (because there are a total of five digits to the right of the decimal points in the two multipliers).

When you have a one-digit multiplier, you're doing "short" multiplication, not "long," so Method 2 doesn't apply here.

See Convert Binary to Octal Number .

No. Multiplication is really just a simplified form of addition. It always involves adding.

The process is the same. You wind up with four partial products to be added together.

Other than using a calculator (or an old adding machine), this is the easiest process ever devised for multiplication.

if you don't carry the number., you'll get the wrong answer because it will become longer than it is supposed to be, like 102 x 5 would be 510 but if you don't carry the extra number, it will be the wrong answer.

The point of having the multiplication table is to be able to multiply quickly. If you don't memorize that table, you will be consigned to a lifetime of very slow multiplication.

See Do Long Division .

The process is exactly the same as with one-digit divisors. You're just dealing with larger numbers.