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the first thing you should do here is rephrase the question. big takeaway: if you see the ABSOLUTE VALUE OF A DIFFERENCE, you should recast it as the DISTANCE BETWEEN THE TWO THINGS on the number line.
therefore, |y - a| is the distance between y and a, and so on.
hence:
QUESTION: is y closer to a than to b ? (1) z is closer to a than to b (2) y is closer to a than z is to b
statement (1): note that the distance y-a is less than the distance z-a, because y is placed between a and z. also, note that the distance y-b is greater than the distance z-b, since z lies between y and b. therefore: distance y-a < distance z-a < distance z-b < distance y-b (note that these are color-coded to the statements above) so, distance y-a < distance y-b "yes" SUFFICIENT
statement (2): same thing as statement (1), except for the second term of the inequality above isn't there anymore. i.e., distance y-a < distance z-b < distance y-b. SUFFICIENT
ans = (d)
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