TenMarks teaches you how you can multiply decimals.
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Learn about Multiplication of Decimals Learn about how to multiply whole numbers or fraction with decimals. We’ll use two different problems to illustrate our point. The first is -5.2 which is a decimal number multiply it by a whole number which is -5. Now, the first thing we’re going to do is convert this particular decimal into a fraction. So since this is got -5.2—let’s learn how to write this is a decimal. Since I’ve got one decimal point what we do is we put the number one below and add as many zeros as there are digits after the decimal point. Here, there’s only one digit for the decimal point so I added only one zero and the numerator becomes exactly what it was without the decimal—I remove the decimal so this becomes -52/10. So now that I know that expression becomes -52/10 multiply it by -5. Now, that I have both of them this way I can multiply the numerators, -52 times -5 is positive 260. Two negatives when multiplied make a positive and the denominator is 10, 260/10 is 26. Let’s try the second one. Second one is, -0.07X4.6 which -0.07 multiplied by 4.6. So let’s do the same principle again. -0.07 becomes in fraction, I’ve got two digits after the decimal so I’ll have two zeros after the one and the top becomes -007 or -7 leading zeros have no value. Similarly 4.6 becomes, one digit after the decimal so this will be 10 and the top will be 46. So now, let’s create a little bit more space since I’ve expressed both of this as fractions the expression becomes -7/100 multiplied by 46/10. These have different denominators so the first thing I have to do before I multiply them—actually no, I can multiply them. I can do the numerator times the numerator so 7x46 is 322, a negative with a positive will remain a negative and 100x10 is 1000 so it’s -322/1000. Now, since I’ve got three zeros at the bottom I can move the decimal spot three digits to the left so this becomes minus 0.322. All I did was because I was dividing by a 1000 I can move the decimal spot three digits to the left because there are three zeros. So to quickly recap what we’ve learned. If we’re multiplying decimal with a whole number first we convert the decimal to a fraction then we multiply one fraction with the whole number, whole number is the same as fraction divided one anyway and we multiply the numerators and the denominators to have the ultimate answer. If we are multiplying two decimals I can convert both to fractions, multiply them and convert them back to a decimal.
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