GRE Exam Numerical Ability Algebra

If a² – ab = 2b², which of the following could be b/a ?
I. 1/2
II. 2
III. -1

(A) I only (B) II only (C) I and II (D) I and III (E) II and III

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GRE Other Question

If ab=x, and a/b=y and ab does not equal zero, then a² − b² = ? (A) x(y-1)(y+1)/y (B) xy - (x/y) (C) x² - y² (D) (y+x)(y-x)/x A survey was sent to 80 customers, 7 of whom responded. Then the survey was redesigned and sent to another 63 customers, 9 of whom responded. By approximately what percent did the response rate increase from the original survey to the redesigned survey? (A) 2% (B) 5% (C) 14% (D) 28% (E) 63%