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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 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)/4d) 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

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

USA
2399 Posts

 Posted - 03/13/2009 :  22:21:41 quote:Originally posted by mingshumThank 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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