testing header
Math Goodies is a free math help portal for students, teachers, and parents.
Free Math
Newsletter
 
 
Interactive Math Goodies Software

Buy Math Goodies Software
testing left nav
Math Forums @ Math Goodies
Math Forums @ Math Goodies
Home | Profile | Register | Active Topics | Members | Search | FAQ
Username:
Password:
Save Password
Forgot your Password?

 All Forums
 Homework Help Forums
 Standardized Test Preparation Help
 tactic 6: replace variables with numbers
 New Topic  Reply to Topic
 Printer Friendly
Author Previous Topic Topic Next Topic  

mingshum
Senior Member

USA
29 Posts

Posted - 03/11/2009 :  16:33:26  Show Profile  Reply with Quote
In my Barron's SAT prep book, the tactic of replacing variables with easy-to-use numbers was used in this example:

If the sum of four consecutive odd integers is s, then, in terms of s, what is the greatest of these integers? so using the numbers 1,3,5,7 = s= 16 and the largest integer is 7 so the choices were:

a) (s-12)/4 b) (s-6)/4 c) (s + 6)/4 d)(s +12)/4 e) (s +16)/4

d) is the only correct answer when s =16 and 7 is the largest integer.

Why doesn't this tactic work with this problem? If the sum of five consecutive integers is S, what is the largest of those integers in terms of S? I used 1,2,3,4,5(answers C,D were correct) and also 2,3,4,5,6 (answers B and E were correct.)?
Go to Top of Page

skeeter
Advanced Member

USA
5634 Posts

Posted - 03/11/2009 :  18:55:02  Show Profile  Reply with Quote
the answer choice would be different ...

for five consecutive integers ...

S = x + (x+1) + (x+2) + (x+3) + (x+4)

S = 5x + 10

(S - 10)/5 = x

(S - 10)/5 + 4 = (x + 4)

(S + 10)/5 = (x + 4)

in the example problem, the correct answer choice was "engineered" to work with the sum of four odd consecutive integers, not five consecutive integers.
Go to Top of Page

mingshum
Senior Member

USA
29 Posts

Posted - 03/13/2009 :  16:19:37  Show Profile  Reply with Quote
Thank you Skeeter...

So under what conditions would you use this tactic of replacing variables with numbers?
Go to Top of Page

sahsjing
Advanced Member

USA
2399 Posts

Posted - 03/13/2009 :  22:21:41  Show Profile  Reply with Quote
quote:
Originally posted by mingshum

Thank you Skeeter...

So under what conditions would you use this tactic of replacing variables with numbers?


Use your own example: 1, 3, 5, 7. S = 16
(s+12)/4 = 7.


Edited by - sahsjing on 03/13/2009 22:22:32
Go to Top of Page
  Previous Topic Topic Next Topic  
 New Topic  Reply to Topic
 Printer Friendly
Jump To:
Math Forums @ Math Goodies © 2000-2004 Snitz Communications Go To Top Of Page
This page was generated in 0.04 seconds. Snitz Forums 2000
testing footer
About Us | Contact Us | Advertise with Us | Facebook | Blog | Recommend This Page




Copyright © 1998-2014 Mrs. Glosser's Math Goodies. All Rights Reserved.

A Hotchalk/Glam Partner Site - Last Modified 21 May 2014