If x + 1/x = 7, then x2 + 1/x2 = ?
----------------------------------------------------------上期答案： Answer: (e) Solution: Gold concentration = weight of gold/total weight 0.80 = (20 • 0.60 + x)/( 20 + x) 12 + x = 16 + 0.8x 0.2x = 4 x = 20 grams
A jeweler has a 20 gram ring that is 60% gold and 40% silver. He wants to melt it down and add enough gold to make it 80% gold. How many grams of gold should be added?
(a) 4 grams (b) 8 grams (c) 12 grams (d) 16 grams (e) 20 grams
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,.上期答案：(b) 420.
In △ABC, AB = BC = 29, and AC = 42. What is the area of △ABC?
(A) 100 (B) 420 (C) 500 (D) 609 (E) 701
------------------------------------- 上期答案： 共有 119 阶。
