Math Made Easy: Adding and Subtracting Fractions With Different Denominators
Friday, September 4th, 2009
In this video, I’ll show you how to add and subtract fractions with different denominators. This process is very different when the denominators are different, but with practice can be just as easy as when the denominators are the same.
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Duration : 0:8:54
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Access full lesson containing this video at: http://www.yourteacher.com/prealgebra/addingdecimals.php Students learn to add decimals by first lining up the decimal points, then adding the numbers by column. For example, to add 14.2 + 2.86, first line up the decimal points, then add the digits in the hundredths column, to get 0 + 6, or 6, then add the digits in the tenths column, to get 2 + 8, or 10, so write a 0 in the tenths column and carry the 1 to the units column, then add the digits in units column, to get 1 + 4 + 2, or 7, then add the digits in the tens column, to get 1. So 14.2 + 2.86 = 17.06.
Access full lesson containing this video at: http://www.yourteacher.com/prealgebra/subtractingdecimals.php Students learn to subtract decimals by first lining up the decimal points, then subtracting the numbers by column. For example, to subtract 9.514 — 1.6, first line up the decimal points, then subtract the digits the thousandths column, to get 4 - 0, or 4, then subtract the digits in the hundredths column, to get 1 — 0, or 1, then subtract the digits in units column, by borrowing a 1 from the 9 in the units column (which leaves an 8 in the units column), to get 15 — 6, or 9, then subtract the digits in the units column, to get 8 — 1, or 7. So 9.514 — 1.6 = 7.914.
Access full lesson containing this video at: http://www.yourteacher.com/geometry/subtractingintegers.php Students review the addition and subtraction of integers using a number line, where a positive integer represents a move to the right, and a negative integer represents a move to the left. Students learn that minus a negative can be thought of as plus a positive.
Access full lesson containing this video at: http://www.yourteacher.com/prealgebra/subtractingmixednumbers.php Students learn to subtract mixed numbers by first subtracting the fractions, then subtracting the whole numbers. For example, to subtract 6 1/3 - 4 2/3, first subtract 1/3 � 2/3. However, notice that 1/3 � 2/3 equals a negative fraction. In this situation, the first fraction, 6 1/3, can be rewritten as 5 + 1 1/3, or 5 + 4/3, or 5 4/3. Therefore, the original problem, 6 1/3 - 4 2/3, can be rewritten as 5 4/3 - 4 2/3. Now, subtract the fractions, 4/3 � 2/3, to get 2/3, and subtract the whole numbers, 5 �4, to get 1. So 5 4/3 - 4 2/3 = 1 2/3. Note that some of the problems in this lesson also require the student to find a common denominator for the fractions. For example, 8 5/16 - 1 1/8.
Access full lesson containing this video at: http://www.yourteacher.com/prealgebra/subtractingwholenumbers.php Students learn to subtract numbers with two or more digits, such as 985 - 47. The first step is to line up the numbers vertically so that the units digits are in the same column. Next, subtract the units digits, the tens digits, and the hundreds digits. When subtracting the units digits, notice that it is not possible to subtract 7 ones from 5 ones, so 1 ten must be borrowed from the tens column, leaving 7 tens and 15 ones. Now, subtracting the units digits, 15 - 7 = 8, subtracting the tens digits, 7 - 4 = 3, and subtracting the hundreds digits, 9 - 0 = 9. So 985 - 47 = 938. Note that the answer to a subtraction problem is called the difference, so the difference of 985 - 47 is 938.
Access full lesson containing this video at: http://www.yourteacher.com/algebra1/subtractingrationalexpressions.php Students learn that when subtracting rational expressions, the first step is to change the minus sign between the terms to a plus sign, and change all the signs across the numerator of the following term. Next, factor each of the denominators, if possible, then give each term a common denominator by multiplying the numerator and denominator of each term by the appropriate value. Next, add across the numerators and keep the denominators the same. Finally, factor the resulting numerator, if possible, to determine if the rational expression can be reduced.