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About Josh
Expertise
When I work through problems, I emphasize principles and key ideas which I believe are worth noting. I will try to answer questions in the following areas, but not at the advanced level. Algebra. Sequences & Series. Trigonometry. Functions & Graphs. Coordinate Geometry. Quadratic Polynomials. Exponentials & Logarithms. Basic Calculus. Probability, Permutations and Combinations. Mathematical Induction. Complex numbers. Physics problems.
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Experience:
I have worked as a teaching assistant in college. My hope is that more people will share knowledge without boundary, give help without seeking recognition or monetary rewards.
Supplementary Website:
See a selection of past questions in my maths repository under "Question Archive"
Education Credentials:
Bachelor degree in Engineering Science.
"Everyone struggles with something."
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You are here: Experts > Science > Math for Kids > Basic Math > Math
Expert: Josh - 8/28/2008
Question
Add and simplify
7/10 + 5/8 + 7/20
Answer
Aimee,
To add fractions together you need to know about "common denominators". Please look up "least common multiple" or "lowest common multiple" (LCM) on a search engine to find out more.
In this question, 40 is the LCM of 10, 8 and 20. That is to say, 40 is the smallest integer divisible by 8, 10 and 20.
Note that 8x5=40, 10x4=40 and 20x2=40.
Also, 4/4, 5/5 and 2/2 are all identical to 1.
So, we can multiply (7/10) by (4/4) without changing the ratio represented by the fraction. We get (7/10)x(4/4) = (7x4)/(10x4) = 28/40.
Similarly, we can multiply (5/8) by (5/5) to get (5x5)/(8x5)=25/40 without changing the ratio represented by the fraction (5/8).
We do the same, multiplying (7/20) by (2/2) to get 14/40.
The whole point is to ensure that they all have the SAME denominator.
7/10 + 5/8 + 7/20 is the same as
28/40 + 25/40 + 14/40 which we can write as
(28+25+14)/40 this simplifies to
67/40
Check out some websites, look at some examples and practice heaps if you are new to this. Good luck!
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