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Marta bought several pencils. If each pencil was either a 23-cent pencil or a 21-cent pencil, how many 23-cent pencils did Marta buy?
(1) Marta bought a total of 6 pencils.
(2) The total value of the pencils Marta bought was 130 cents.
ANS: B
想請問一下, 怎麼不是C呢? 從2)看來23x+21Y =130. 兩個未知數但只有一個equation. 以DS類型的題目來說, 看到這種兩個未知數但只有一個equation的不是就直接可以assume 是insufficient嗎? 也許這題因為X跟Y都必須是integer所以 X跟Y只可能有一個答案, 可是要帶很多不同的interger下去try才有答案. 會花很多時間. 真正考試時每題都必須這樣嗎? 還是有什麼比較快的方法? 請指教!!