Question

好心人帮忙解答

The R students in a class agree to contribute equally to buy their teacher a birthday present that costs y dollars.If x of the students later fail to contribute their share, which of the following represents the additional number of dollars that each of the remaining students must contribute in order to pay for the present?
A、y/R B、Y/R-x C、xy/R-x D、xy/R(R-x ) E、y/R(R-x)
答案选D，求解

Answer 1

答案是选D。
解答：原本R个学生，每个人应该付y / R，但实际只有（R-x）个学生付了钱，一共付了y(R-x) / R ；此时还差y - { y (R-x) / R} 这么多钱才能买到礼物；所以付了钱的学生每人还要多付 [ y - { y (R-x) / R} ] / (R-x) 的钱，简化后为答案D，才可以买到礼物。
其实题目是问付了钱的学生每个人还要再多付多少钱才可以买到礼物，而不是问还没付钱的学生每个人要付多少钱（选A）才能买到礼物。