what is a very simple formula for finding the least common denominator to add/subtract fractions?
541370
Multiplying the denominators of all the fractions would be the easiest method.\n\nHowever, if the numbers are really big and you prefer working with small ones (e.g. if you do not have a calculator), you can first find the lowest common multiple (LCM).
96822
E. None of the above.\n\n1/10 + 1/4 + 1/5 + 2/5.\n\nUse 20 as the common denominator.\n\n2/20 + 5/20 + 4/20 + 8/20 = 19/20.\n\n19/20 is not one of the answers.
215144
Multiply the numerators together.  Then multiply the denominators together.  Just go straight across.  If you want, you can simplify the fractions in the beginning so that it's a bit easier.  Then if your answer isn't in lowest terms, I'd simplify that too.  Hope I helped!
208764
This is actually elementary math. If you remember the order of operation, it helps. \n\nStep 1: Do the part of the problem in the parenthesis.\n  Example: (4/3)= 1.3333333333 (you get where this is going)\n\nStep 2: Take that answer and multiply it by the named multiplier.\n  Example: 1.33333 * 12= 16\n\nStep 3: Take the result of that transaction and devide it by the named devisor. For this method don't use the fraction way, and don't use a calculator. Do a basic devision problem like you were taught in the 3rd grade using the "bracket."\n  Example: 16/13 = 1  (13 goes into 16 1 time)\n\nStep 4: Subtract the 13 from the 16 and it will give you your remainder.\n  Example: 16/13 = 1   16-13= 3\n\nThe answer when written correctly isn't with a decimal but would look like this- 1 R3.\n\nAlso for a little note for this- Order of operation:\nP (parenthesis)\nE (exponents)\nM (multiply)\nD (devide)\nA (addition)\nS (subtraction)\n\nHope this helps!
922233
You start with [3-(a/b)] / (a/b)\n\nTo get a/b out of the denomenator, multiply the top and bottom of the fraction by b/a:\n\n[3-(a/b)] * (b/a) = (3b/a) - (ab/ba) = (3b/a) - 1\n\nNow find common denomenators:\n\n(3b/a) - (a/a) = (3b - a) / a\n\nand there's your answer:\n\n(3b - a) / a
1079568
Find the least common multiple for 4 and 8.  It is 8.\nMultiply everything by 8\n8(10x) - 8(1/4) = 8(9x) + 8(3/8)\n80x - 2 = 72x + 3\nSubtract 72 x from each side\n8x - 2 = 3\nAdd 2 to each side\n8x = 5\nDivide each side by 8\nx = 5/8
784219
The lowest common multiple, or LCM, of 2 integers is the smallest integer that divides boths\n\nTo work out the LCM of any numbers follow these steps:\n\n1)Prime factorise the numbers\n\n2)Then match the prime divisors of the 2 integers by inserting, if necessary, and primes raised to the power of 0\n\n3)The LCM is the product of all the primes, each raised to the largest exponential\n\nIn this case 35 = 5*7 and 12=2^2*3\n\nThe LCM is 2^2*3*5*7=420
650911
When you're given a ratio, you can find an equivalent ratio by multipying or dividing both elements of the ratio by the same number.  For instance, 3:4 = 6:8 (I multiplied both the 3 and 4 by 2... 3x2=6, 4x2=8).\n\nKeeping that in mind, we want to find a simpler way to write the given ratio, and our strategy here will be to find the lowest common denominator (LCD) of the two fractions, and multiply both fractions by that integer.  (If multiplying a fraction times a non-fraction (the LCD) throws you, write the LCD as a fraction by giving it a denominator of 1.)\n\nSo, all you need to work out is:\n\n(1) what's the LCD of 1/3 and 2/5?\n\n(2) when I multiply 1/3 and 2/5 by that number, what do I get?\n\nGood luck!
762985
(b-4)/(b-4)(b+4) simplifies to 1/(b+4)\nrestrict denominator...bcannot equal 4 or -4
965696
Two add two fractions, the denominators must be equal.\n\nThe first step is to convert the addend that is a mixed number (an integer plus a proper fraction) into an improper fraction. Do this by multiplying the integer part by the denominator and then add the numerator of the fraction.\n\nExpress the result as an improper fraction (fraction with value greater than 1) whose numerator is the sum you just calculated and whose denominator is the same as the denominator of the fraction part of the mixed number.\n\nFor example: 2/3 + 4 2/5 = 2/3 + 22/5\n\nNext, find the least common denominator of these two fractions, the smallest integer that contains both denominators as factors. For the example above, this is 15. Multiple both terms by (3*5)/15, which equals 1, and therefore does not change the value of the fraction:\n\n(2/3) * (3*5)/(15) = 10/15 (the 3's "cancel out" since 3/3 = 1)\n(22/5) * (3*5)/(15) = 66/15 (the 5's "cancel out" since 5/5 = 1)\n\nNow add 10/15 + 66/15 by adding the numerators and keeping the same denominator: 76/15.\n\nFinally, express this improper fraction as a mixed number by dividing: 5 1/15
980475
13/16 - 1/4 is like 13/16 - 4/16 which equal 9/16\n\nYou just have to get the denominators equal to add or subtract fractions...so just multiply the the top and bottom of 1/4 by 4 and you get 4/16 (which is the same as 1/4). It works the same for all fractions that you want to add or subtract.
1135639
(1 - a/b) divided by (a^2/b^2 - 1)\nGet a common denominator for 1 - a/b\n1 - a/b\n= b/b - a/b\n= (b-a)/b\nGet a common denominator for a^2/b^2 - 1\na^2/b^2 - 1 \n= a^2/b^2 - b^2/b^2\n= (a^2-b^2)/b^2\n= (a-b)(a+b)/b^2\n\n(b-a)/b divided by (a-b)(a+b)/b^2\n= (b-a)/b times b^2/[(a-b)(a+b)]\nCancel anything on the top with anything on the bottom.  Note that a-b = -(b-a).\nAnswer: -b/(a+b)
802171
The earliest know mention in literature of common denominators (least common multiple) was Thomas Blundeville in his 1594 publication "Exercises" where he says, "Multiply the Denominators the one into the other, and the Product thereof shall bee a common Denominator to both fractions." The term Least common multiple is found in 1823 in J. Mitchell, Dict. Math. & Phys. Sci.: "To find the least common Multiple of several Numbers"
831251
This problem is kind of neat. We have two fractions in a compound fraction - one in the numerator and one in the denominator. Since both fractions have the same denominator:\n\n(x + 4y)/y and (x + y)/y\n\nWe can eliminate the y's and form a fraction out of the numerators. Note that we can only do this because the denominators are the same.\n\nSo the original expression equals:\n\n(x + 4y)/(x + y)\n\nAnother way to do this is to multiply the fraction in the numerator by the reciprocal of the fraction in the denominator.\n\n(x + 4y)/y * y/(x + y) =  y(x + 4y) / y(x + y) = (x + 4y) / (x + y)
100703
Find the lowest common denominator.\nThe lowest common denominator is 20.\n\nAdd the increment hours together.\n5 plus 4 is 9.\n\nDivide the lowest common denominator by the increments.\n20 divided by 9 is 2.22222.\n\nSo the answer is 2.22222 hours.
843077
Who sez?  You need a common denominator to ADD two fractions.  To multiply, just do separate operations on the numerator and denominator.
289395
Find the commone denominator, and then convert both fractions into their equivalents using that denominator.  For example, 1/2 can also be written as 2/4, 3/6, 4/8, etc.  Once both fractions have the same denominator, just add the numerators and reduce.\n\nTo add 1/3 + 4/9, the common denominator is 9.  4/9 is already done, so you would just need to change 1/3.  3 goes into 9 3 times, so multiply the top and bottom by 3 (or multiply by 3/3, which is the same as multiplying by 1 - perfectly legal in math :) 1/3 * 3/3 = 3/9\n\nNow you have 3/9 + 4/9 = 7/9 --- this cannot be reduced any further.