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by nidhis.1408 » Fri Jul 06, 2012 9:32 am
If c +d = 11 and c and d are positive integers, which of the following is a possible value for 5c +8d?
(A) 55
(8) 61
(C) 69
(D) 83
(E) 88
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by tutorphd » Fri Jul 06, 2012 10:06 am
5c + 8d = 5(c + d) + 3d = 55 + 3d

subtract 55 from each answer and see if it gives a multiple of 3 = 3d
if it does, calculate the value of d, it should be in the range:

dmin = 1 (d is a positive integer)
dmax = 10 (c is at least 1)

only the answer 61 works.
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by Bill@VeritasPrep » Fri Jul 06, 2012 5:37 pm
tutorphd wrote:5c + 8d = 5(c + d) + 3d = 55 + 3d

subtract 55 from each answer and see if it gives a multiple of 3 = 3d
if it does, calculate the value of d, it should be in the range:

dmin = 1 (d is a positive integer)
dmax = 10 (c is at least 1)

only the answer 61 works.
That is a really clever approach!
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