Find the Number
Date: 05/14/97 at 16:04:13 From: Erin Warner Subject: Number Word Problems (algebraic phrases and equality) Five times a certain number is six less than three times the same number. What is the number?
Date: 05/20/97 at 10:28:33 From: Doctor Edwards Subject: Re: Number Word Problems (algebraic phrases and equality) Erin, First I'll show you how to solve similar problems, and then you can try to use the same method on yours. Example 1: 4 times a certain number is 8. What is the number? Let's rewrite this as a math equation. In place of "a certain number," I'll use a variable, X. X can be anything, but in this case it will be the answer I'm looking for. Now I can translate the words in the problem into: 4 * X = 8 To find out what X is, I need to undo everything that is being done to it. In this example, it is being multiplied by 4. When I divide by four, I have to be careful because I have to divide the things on each side of the "=". I can change my equation to: 4 * X 8 -------- = --- 4 4 Then to: X = 2 Now I have my answer: the number is 2. Example 2: 4 times a certain number is 9 more than the same number. What is the number? This time, my equation will be different: 4 * X = X + 9 This problem is harder because I have an X on each side of the equation and I need them to be on the same side. If I subtract an X from both sides, the right side will become 9, and, since I am subtracting one X from 4 X's on the left, it becomes 3 X's, or 3 * X. Now my equation is: 3 * X = 9 Now this problem is very similar to the first one. I will divide both sides by 3, to get X = 3. To solve your problem you need to come up with an equation, with X representing the number you don't know. Then you need to try to change the equation so that X is alone on one side of the "=" and a number is alone on the other side. That number will be the answer. One last hint: think of '5 * X' as 5 X's and '3 * X' as 3 X's. If you need more help, write in again. -Doctor Edwards, 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.