Algebra using Fractions
Date: 5/27/96 at 23:48:13 From: Leslie Besman Subject: Algebra using Fractions Dr Math, I need you to answer this question and then show me how you did it: 5 - X = 9 8 Leslie Besman Northern Lights College, Dawson Creek, BC. email@example.com
Date: 5/30/96 at 14:30:32 From: Doctor Mike Subject:Re: Algebra using Fractions Hello Leslie, First, let me be sure I understand your question. In words, I think you mean "If the fraction (5/8) times the unknown X is equal to 9, then what number does X have to be?" Is that right? The value of X is 14.4 in decimal form, which is the same as 72/5 in the form of a fraction reduced to lowest terms. The expert didn't have to be an Einstein to get that answer for you. One of the most important BUT ALSO MOST SIMPLE algebraic ideas is that if an equation is true, it is STILL going to be true if you do the same thing to both sides of the equation. In this case "the same thing" is to multiply by (8/5). Here's what I mean: 8 5 8 - * - * X = - * 9 5 8 5 The (8/5) times (5/8) on the left equals one (1). You can tell this just by what you probably call "cancellation", or also because multiplying those two fractions together gives 40 divided by 40. So, the left side is just the unknown X all by itself, and the right side is a simple arithmetic task. I hope this helps! -Doctor Mike, The Math Forum Check out our web site! http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.