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How much did it cost?

stephanie spent $79 she bought a skirt, a t-shirt and a pair of shorts. She paid $9 more for the t-shirt than for the shorts, and $7 more for the skirt than for the t-shirt. how much did the skirt cost her?
 
answer is $34. 
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2 Answers

Charlie:
 
Let the cost of the shorts (least expensive) be x dollars.
The cost for the t-shirt is $(x+9).
The cost for the skirt is $(x+9) + 7 for the skirt.
Her total cost is x + x + 9 + x + 9 + 7 = 3x + 25 dollars.  We are given that this total cost is $79
So, equating, we get  3x + 25 = 79, that is 3x = 54.  Hence x = 18, the dollar cost of the shorts.
 
The dollar cost of the skirt is therefore 18 + 9 + 7 = 34.
 
Dattaprabhakar (Dr. G.)
Let s = value of the skirt, t = value of the t-shirt, and p = value of the pair of pants.
 
79 = s + t + p
 
t = 9 + p  ⇒  p = t - 9
 
s = 7 + t  
 
Substitute p and s into the first equation and you should get t = 27.  So the skirt costs s = 7 + 27 = 34.