Author 
Topic 

mingshum
Senior Member
USA
29 Posts 
Posted  03/11/2009 : 16:33:26

In my Barron's SAT prep book, the tactic of replacing variables with easytouse 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) (s12)/4 b) (s6)/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.)? 


skeeter
Advanced Member
USA
5634 Posts 
Posted  03/11/2009 : 18:55:02

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. 


mingshum
Senior Member
USA
29 Posts 
Posted  03/13/2009 : 16:19:37

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


sahsjing
Advanced Member
USA
2399 Posts 
Posted  03/13/2009 : 22:21:41

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 



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