Translating English to AlgebraDate: 06/27/2002 at 22:38:06 From: Nicole Weaver Subject: algebraic expression Write an algebraic expression for Seven more than twice a number. The problem I am having is to determine how to differentiate between more than/less than as in inequalities, or plus and minus. Date: 06/28/2002 at 12:55:35 From: Doctor Peterson Subject: Re: algebraic expression Hi, Nicole. The difference is that "greater than" and "less than" in inequalities are really verbs: "7 > 2N" means "seven IS MORE THAN twice a number". What you are given is not a complete sentence like that (with a verb), but just a phrase. Phrases correspond to expressions in math. In fact, if you are told to write an expression, you will NEVER have to use ">" or "<", because they don't go in expressions! If I said "My age is seven more than twice her age", I have used a phrase equivalent to the one you are given. How would I interpret it? If I knew her age (say, 14), I could find my age by doubling her age (to 28) and then adding 7 (making 35). I added 7 because I know that my age is not just "more than" her age, but "seven more than" her age, meaning that I have to add 7 to hers to get mine. Now to write an expression for this, I just take a variable, say N, and do to it just what I did to the presumed age a moment ago. I start with N, then double it to get 2N ("twice a number"). Then I add 7 to it to get 2N+7, which is seven more than 2N. Taking it step by step this way, and thinking through how you would calculate a value if you knew the starting number, allows you to build the expression piece by piece. Does that help? - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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