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 Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion

 September 24th, 2010, 09:26 PM #1 Newbie   Joined: Sep 2010 Posts: 1 Thanks: 0 please help adding fractions??? What are the steps? I've been on this for 7 days and don't know what to do. Like if there's 1/7+4/8= lcd is between 41 or 40 for this problem? Like I know you're supposed to find the lcd for the bottoms to get a common denominator, but when you find the lcd what's next ??? September 24th, 2010, 09:54 PM #2 Senior Member   Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs Re: please help adding fractions??? First, we should reduce both fractions if possible to simplify the process, so we work with the smallest numbers we can. 1/7 is fully reduced, but 4/8 may be written as 4/(2�4) = 1/2 So we have 1/7 + 1/2. The two denominators share no common factors (both are in fact prime) so the lcd will be 2�7 = 14. Begin with 1/7 and ask yourself what the denominator 7 must be multiplied by to get 14, and as we saw, that is 2. So we need to multiply 1/7 by 1 (so we don't change its value, only the way its represented) in the form of 2/2. (1/7)(2/2) = 2/14 Now, consider 1/2. What must the denominator 2 be multiplied by to get 14, which is 7. So as before we multiply by 7/7. (1/2)(7/7) = 7/14 Now, our two fractions have a common denominator, and we can directly add them together. 2/14 + 7/14 = 9/14 Notice how the numerator is the sum of the original denominators and the denominator is the product of the original denominators?  September 25th, 2010, 04:28 PM   #3
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Quote:
 Originally Posted by alternap18 . . . you're supposed to find the lcd for the bottoms to get a common denominator . . .
You need to use a common denominator, but it needn't be the LCM (least common multiple) of the original denominators. Any other common multiple of the denominators could be used instead.

For example, 5/6 - 7/10 = (5/6)(5/5) - (7/10)(3/3) = 25/30 - 21/30 = 4/30 = 2/15,
or . . . 5/6 - 7/10 = (5/6)(10/10) - (7/10)(6/6) = 50/60 - 42/60 = 8/60 = 2/15. Tags adding, fractions Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post jmon117 Number Theory 3 January 31st, 2013 06:34 PM Mike7remblay Algebra 2 July 23rd, 2012 09:36 AM _Mike01 Elementary Math 6 March 1st, 2012 03:09 PM thejared Algebra 5 August 3rd, 2009 08:59 AM cafegurl Elementary Math 6 November 18th, 2008 01:15 PM

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