2. 外语
  3. If the numerator of a certain fraction is doubled and the denominator is decreased by 5, the new fraction is equivalent to 2/3.

If the numerator of a certain fraction is doubled and the denominator is decreased by 5, the new fraction is equivalent to 2/3.

admin2022-05-18  20
问题 If the numerator of a certain fraction is doubled and the denominator is decreased by 5, the new fraction is equivalent to 2/3. If the original fraction is equivalent to 2/7, What is the sum of the numerator and denominator of this fraction?
选项 A、9
B、27
C、45
D、54
E、36
答案C
解析 一个分数等于2/7，并不是说这个分数就是2/7，因为分子分母同时乘以一个倍数会变为另外一个分数，这个分数仍然等于2/7，现在假设分子分母同时乘以n，那么根据题意得到：

解这个等式得到：n=5，所以分子分母之和等于5 x(7+2)=45，C为正确答案。
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